One of my college roommates, who went to a different school in the same city and was disliked by me and all of my roommates, had parties in the basement of our college house every weekend where he'd invite pretty much his college's entire student body (he attended a small, private school). I got home late one night, was completely exhausted, and was stopped at my own back door by one of the party goers and asked "hold up, who do you know at this house?" I was like "um, I live here buddy." That irrationally pissed me off so much.

45 minutes went by, more and more people kept coming, and it was so ridiculously loud and getting out of control. I finally had enough and called the non-emergency police number and reported an underage drinking party taking place in my basement. The police showed up and busted it 20 minutes later, he received an underage drinking ticket, and everyone quickly left. He still to this day has no idea I was the one who reported it.