Have you ever noticed that
a) £2 coin looks very similar to 2 € coin, because both are big bi-colored coins, and
b) £5 looks almost like 5 €, because they are both small green banknotes?

Well, I have made myself look like a fool because of this.

Usual me: I forgot to take the euro notes and coins out of my wallet. Then I went to Aldi, selected stuff to buy, removed all my euro coins from my wallet and placed them into my pocket (in order not to mix them!), and waited in a cashier line. My stuff cost £3.25, and I was happy that I had enough coins.

Wait, that's 2 euros, said the cashier lady. I apologized, cursed silently, checked whether there were any more coins left, found no £2 coin, and took out a £5 note.

Wait, euro again, said the cashier lady. So I apologized again, cursed silently again, and gave her £20 instead. I made pretty sure that there was the smiling queen on the note before handing it in.

:-)