I have no pet peeves at festivals. I spend a lot of money to have a great time while I'm there so why would I let what other people do bother me?
But with that said, the beer garden at Chella pisses me off. I don't do drugs anymore so I like to drink a lot while I'm there, and spending time in the beer garden forces me to miss acts. Last year I poured beer in a water bottle and put it in my little backpack and was able to sneak some out. But a beer just isn't as good when you're drinking it from a water bottle.