Is AUTHOR wrong in the post ? POST : I've said I'd go to my best friends for new years eve, as she was super excited to have a few friends over. 
The issue is that this party is shaping up to not be what i expected. There is ~20 people going, its a big extravegant piss up, and shes wanting everyone to give £20 for snacks and booze. However, I don't drink at all after some traumatic experiences at parties, I don't like loud pop music, and I'm extremely uncomfortable in the presence of strangers. I'm going to be the only sober person and I don't really want to pay for everyone's drinking habits.

I have a friend of my boyfriend who has invited us to his house for a small (free) 6 person movie night. Which will be nice and calm and my cup of tea.

Am I the asshole if I tell my best mate I'm going to this movie night instead of hers as just the thought of her party is making me anxious. 
