what wrong with the chairs?

it looks like they are trying to take a shit.

Is the floor lava?

One person started doing it and then, in true Chinese tradition, they all copied it.

the asian squat seems to have a long history over there. i doubt this is really a new thing.

it must be some guy thing, being cool and stuff. Girls are sitting all right.
could also be Ninja related.

Probably scared of the rats running around

its a way to eat less... when your legs are pressed on your stomach. why else do you think they are all so small and thin?

The surface of the chairs were filthy after those students who put their foots on it probably for setting up a cool posture. They did that everyday so the chair could not be sitten anymore and they are disinclined unusually to clean them.