Running out of something you swore you had more off. Also someone shouting at you while you're nodding or buzzing heavily.
I think the worst buzzkill I've had is doing NO2 (whippets, laughing gas, etc.)
When someone decides to try and have a conversation with you right as you're peaking, because they did earlier than you and don't have anything to do now. WTF? The high's only like 10 seconds, leave me alone!
Having to clean up someone's vomit sucks ass. When you're in a group trip and one person starts freaking out for no reason and now the focus of the group is to cheer up said person. The worst buzz kill I've ever experienced though was when my (ex)friend pulled out a 4 inch blade with a head full of DOx, because he thought our other friend was coming up the stairs to kill us.
So I was just wondering what you guys think are the biggest buzz kills, and yes we all understand if you're one to smoke in a house and the parents come in; and getting caught by the police, we all know those. Anything else?