What nasty and not widely known customs are there in your countries?

They did this at my high school when someone would drop a tray in the cafeteria.

In Sweden, if you lean out a window at night and scream, other people will open their windows and scream with you. (this is only in big cities, though)

In Straya, when someone drops a glass, plate etc (Anything that ends in breakage on the floor), we shout 'Tax-iiiiiiiiiiiii'.
(Indicating the person is drunk and needs a taxi home)

In the Netherlands we squat down and shit on the floor if someone makes a bad pun

In Australia we imprison refugees on an island nation in conditions that break the UNs laws. Haha so zany

In Greece, we "spit" people when complimenting them, to keep the "bad eye" (=negative energy) away

Dude that happens here in Germany too

I think that's an everywhere thing.

Wonderful, I'm moving to Poland. Applause shall follow me wherever I go.

Oh come on, that's not true at all

In America, if something does something stupid or makes a fool out of themselves, everyone in the immediate vicinity will simply pull out assault rifles and shoot them to pieces. I know it's kinda weird, but that's just how it is out west :))))))

Poland? All my friends do it and we are all different nationalities

Here in SL everyone gasps and one of them asks if they could have the biggest piece of the item that was broken