Drinks in the pub whilst dressed up like an idiot! The hangover is the worst part, especially when I was supposed to write an essay today.
EDIT: Also, what is with everyone downing Halloween. Okay, so it may just be a way of people to make an easy couple of quid selling plastic masks and themed sweets but really, you don't have to shell out any money to these people if you don't want to. My costume didn't cost me a penny and I had a good night out. What is not to love about that?