Do we know what the blood alcohol level was of the teenagers in question?
Where they "drinking to hilarity" or were they actually drunk?
Just a single drink can make an inexperienced drinker feel "different" -- less inhibited, more "fun", more talkative, easier to laugh, etc. We're talking a single beer or wine cooler, or even part of one!
I'm sure you agree, Telesphorus, that alcohol is not forbidden to Catholics as long as one does not drink to excess.
It's hard to tell that someone was "drunk" just by looking at a picture of them -- unless they look s###-faced.
But a smile on their face? Much more inconclusive.