My folks always harped about underage drinking being against the law and how some kids somewhere else got kinda sick from drinking too much and blah blah.. none of that shit ever once phased me. You'll have to let them get shitass wasted puking into eachothers faces for hours then wake them up at 5am the next morning banging a baseball bat in a metal bucket.. then give them a big fat "I told ya so"
That is the only way to get thru to kids.