Do you know any funny customs or taboos?

Question

Do you know any? I know one. Kissing in train stations in france are illegal. Im curios.

Answer 1

walking around your apartment naked in Singapore is illegal (but I assume that's only if someone sees you!).

Oral s*x, even between consenting couples, was illegal too until recently ;)

Answer 2

I heard that giving someone a thumbs up sign in the Middle East is the equivalent of flipping them off.