[cstreit]

I'd tell the parents when they got home or call them immediately. Why? You've got to decide who you want to remain friends with, the 18 year old or the parents? How would you feel if the parents found out that you watched their kid throw a drinking party and didn't say anything? How would you feel if it were YOUR kids and the neighbors didn't say anything? I'd be pissed!

I expect my neighbors to watch what my kids do (mind you my son is almost 4, not 18) but the feeling is mutual. That's part of what's great about my area... We all do the same. The next door neighbors 15 year old son and his friends 'hang out' in our culdesac on the weekend nights. I know my neighbor would be pissed if I saw them drinking and didn't tell him.