In America it's even worse because they say "What's up?" in the same way we Brits say "Alright?", but "What's up?" to me like the person has detected something wrong with you and wants to know what the problem is. At least "Alright?" is more generally asking for your status.

Of course, both are generally rhetorical, which must be confusing for some foreigners learning English, especially with the correct response to "Alright?" being "Alright?" and similarly with "What's up?".

I believe the correct response is "Chicken butt," but maybe I'm in very exclusive company in responding that way.