mark out
When you "mark out" you stand up for something or believe something completely. If you're a massive fan of a band and you refuse to let people critize them, you are marking out.

Believing something completely.

Comes from the wrestling term markwhere a smark forgets reading the spoilers, guessing the storylines and bitching about backstage and just feels the moment.
1. Dude, you always mark out for crappy emo bands.

2. Yeah, I totally marked out last night when Foley got thrown off the cage.