What would you do in a such situation?

whoever calls the teacher is a fucking snitch. Help your friend out. bitch slap him for being so dumb if you have to.

Tell him he is going to develop a drinking problem and stop being a fucking moron. who the fuck gets drunk at school?

Black mail him into giving me some alcohol.

If you want to let him know drinking is not the solution to his problems you'll have to do something drastic...

Rape him.

Okay I won't deny, that friend is me... And the other day I attended a class drunk. And my friend was like if he catches me again drinking, he tells the teachers about it.

And it kinda surprised me because I thought a REALLY good friend would try to help a friend... Yeah, try to talk to him and tell him to stop drinking, but if I noticed that my friend's drunk, I wouldn't tell the teachers, knowing that he'll be in trouble... I would rather skip a lesson or two just to be near my friend, to stop him doing something stupid. But seems like that's only me.

Thanks guys.

Tell him to get his act together. Don't go with him, that could make people think you are doing what he's doing and get you kicked off the class.

Tell him to stop being a shit head.

Stage an intervention or get him to a counselor.