when vegeta's hair gets wet...does it fall down または is it the same???

I don't know how but it stays the same like how can his hair do that!

Actually, in the episode where Vegeta takes a シャワー at Bulma's house, it does go down...

I'm not sure, I don't remember the episodes well when his hair gets wet. I think it stays the same.

It stays the same.

it remains the same

beggining of android saga when vegeta wore that ピンク シャツ he took a シャワー and was forced to wear it and in the シャワー it showed his hair going backwards like wind was blowing
(hope this helps)

it gose down

It goes down. For those who get this: The female species, what an enigma!