Long time no post! Sorry for that, many things have happened in past few weeks.

Of course most of these things have been associated with Christmas. I will try to provide some details of English Christmas celebrations below.

1/ The Secret Santa
Very funny thing; maybe you know it and/or do it yourself. We did this in my company with some colleagues. It works like this.
You persuade bunch of people to participate. (I thought this to be difficult, but obviously this is quite popular here and may people like it and participate. In fact, I thought that this was some 'kid's stuff', something that only young people participate in. Then I was heard people from another company talking about who's secret Santa of whom and whether they have this sorted already or not, and they were talking about this stuff in the lift. Which in my opinion means that it's widespread.)
You put their names in a hat; people pick one name from the hat (if they pick their name, they have to give it back and repeat).
Everyone has someone's name, and has to buy a present for that person. (There's usually a cap on spending, to avoid people getting too cheap or too expensive presents.)
Not surprisingly, it was all fun. It showed that some people know some people quite well! Anyway, they know me well, because I got a gift that suits me.

2/ The Christmas parties
Endless. At least three of them in our company (which probably means that there are also at least three of them in any other group, club, sports establishment, etc. etc.).
Our company has a certain very stupid tradition which has to be observed by newcomers. (It's like an initiation.) I did not like it at all; I don't really understand why people are being punished and humiliated for joining the company. But as English people say: hi ho.

3/ Pubs full of people
This is closely connected to the previous point. Everyone is celebrating Christmas with endless parties, and therefore the pubs are exceptionally full, day and night. It all starts in early December, and continues to the Christmas day.

4/ Christmas crackers, crowns, and stuff
This is Christmas partyware. A cracker looks like a giant candy. Everyone gets one cracker. Two people sitting next to each other pull the opposite parts of the cracker. The cracker breaks under the pressure, but asymmetrically, and one of the people gets approx. 2/3 of a cracker - with some hidden little present, while the other person gets nothing. There's also usually a paper crown in each cracker, and these are distributed evenly between the people, so everyone gets one crown.
There are usually also other things on the table, such as balloons (better: elongated, sausage-like balloons, so that people can beat each other with it) and miniature confetti shooters (pull a string, and it 'explodes' and sprays papers on people).
In few words: it's a mess.

5/ Trees (and no carps)
Like in the Czech Republic, Christmas trees are sold on many places, usually directly in the streets. Obviously (as advertised), the prices start at £39. we did not buy a Christmas tree - as usually, we've bought a bottle of whisky instead. :)
There's one thing that is not there in the streets: huge blue tubs with carps. In the Czech Republic, the very traditional Christmas Eve meal is carp and potato salad, and people like to buy the fish absolutely fresh. This means that there are carp-containing tubs in the streets, where sellers have their stalls. You can buy the poor animal alive and kill it yourself, or you can have it killed by the fishermen who sell it. (I prefer the second option, and, frankly, I think that the first option should be banned. People usually don't know how to kill the fish quickly, and in the end it's like animal torture really.)
Well, no surprise that in this turkey eating country, people do not buy fish like this.

6/ Santa's grotto in Arndale shopping centre
Oh yes, there was an enclosed space which looked like something between an odd-coloured Christmas tree and a rock: Santa's grotto. We haven't been inside, but there's allegedly Santa Claus inside, and if you have kids, you can pay approx. £5 to £10 per kid to visit the grotto.
There were also elves, guarding the entrance. I wonder whether it was a coincidence that the elves were young girls with revealing clothes, and the kids were usually accompanied by dads...
(Just for the record: in the Czech Republic, it is not Santa Claus who delivers the Christmas presents. Therefore, I have never done this as a kid.)

7/ Christmas markets
Installed up to 21 Dec, with huge sales on the last weekend. Full of people up to the last moment.
Interestingly, there was a huge hanukkah 'candleholder' just near the Christmas market.

8/ Total shutdown
This country went through an absolute, total shutdown just before Christmas. In the week starting 21 Dec, there were very little cars on the streets, and not many people in the streets. The buses were half empty. Many shops were closed, or were only open for few hours a day. On 24 Dec, which is supposed to be a normal working day here, I went to work, but apparently I was one of the few. Then we were kicked out of the office at 3 pm, which was a nice surprise for everyone but me - I had stuff to do, and wanted to stay until 4 pm!

8/ Christmas Day
...is 25 December. That's funny, because in the Czech Republic, the most important day is 24 Dec (it is a holiday, and presents are unpacked on 24 Dec in the evening). Therefore I am usually confused when people start talking about Christmas Day!
Anyway, absolutely nothing works on 25 Dec. No shops are open, not even the huge ones which are normally open 24/7. There are no buses, and no trams, and no transport at all.

9/ Ho ho ho!
Santa's signature laughter. Can be seen or heard everywhere, written on the shop windows, buses and city halls, and said by barmen, shop assistants, bus drivers, colleagues at work, and everyone. The first thing we have heard on 25 Dec morning was our neighbor next door saying 'Ho ho ho' loudly. The automatic cash desks in Tesco say 'Ho ho ho merry Christmas' even now. O_o

10/ Bah humbug!
If you are disgusted or tired of all the Christmas stuff around, or if you just want to be less mainstream, you can say this instead of 'Ho ho ho' (see above). Many people do. Many shop windows etc. do as well.

11/ Christmas jumpers
Everyone wears funny jumpers with snowmen, reindeer, Santa Claus, elves, elf clothing, Christmas trees, or (the most conservative people) Norwegian designs. This year, some people had Minions dressed as Santa on their jumpers. Sometimes, there are things attached to the jumper: for example, fluffy spherical objects which are supposed to resemble snowballs, or orange pointy things that should simulate snowman's nose, things like that. I have seen a guy who had a transparent pocket for a smartphone in his jumper, and the smartphone showed a fireplace with fire.
If you want to be less mainstream, you can wear 'bah humbug' jumper instead.

11a/ Christmas jumper day
We have had this in our office. Everyone is supposed to wear their ugliest finest Christmas jumper, and donate to Charity. I don't have any suitable Christmas jumper, but my husband has a Swiss jumper (which I gave his as a present when I returned from a skiing trip), and this jumper has some deer and things on it, so it qualifies as Christmas jumper, and I could wear that.
People obviously take this seriously, because when my boss arrived to the office, and found that there was a Christmas jumper day, he went to quickly buy one to the nearest shop.
You are not supposed to wear Christmas jumpers after 6 January.

12/ Ugly Santa near the city hall
There's an incredibly ugly Santa Claus on the main square. I hope it will disappear soon. If we are lucky, it will get damaged, burnt and destroyed during New Year's celebrations.

13/ Christmas cards
Everyone sends or gives Christmas card to everyone else. You send cards to friends, parents, colleagues, doctors, lawyers, customers, suppliers, subcontractors, business partners, neighbours, your dog, and the guy you've met yesterday in Aldi.
The cards are usually quite ugly, with some Christmas kitsch Christmas pictures and things. Sometimes there are (stupid) things written in the cards, and sometimes there is an empty space so you can write your own wishes there.
I myself only gave one real, paper Christmas card, to one of our secretaries who helps me a lot (and I wanted to thank her for all that). I have personally received zero paper cards, and a few e-cards. We (me and my husband together) got two cards from friends in the Czech Republic. Our landlady got approx. zillion cards, in coloured envelopes of funny shapes.
It seems that this card business is a-booming here, they have cards for, like, every occasion. Not only Christmas, but also birthday, weddings, childbirths, new jobs, retirements, moving your house, your kid's first teeth, everything.

All right, that's that. I am kinda glad that it's all over now... but I also hope that next year, I will be able to participate in all this like a real English person! :)