Yeah I guess its because they think it's cool to be drunk, or stoned.
Maybe they think it's mature?....but no I think its more the fact they think it is cool to get drunk....and if your not really that drunk you can pretend to be and people will be impressed...(especially if you still smell of alcohol)....maybe they are thinking they are more drunk than they actually are? like a placebo in a way....

Is acting drunk better than them actually being drunk though?