The guy I work with has a nervous twitch and deliberately cracks his neck every 5 minutes?

I know what you're thinking K-mac and murder is not the answer. Standing behind him quietly and timing it just right so when he twitches you snap his neck is against the law and a minimum of 15 -20 years in prison.

Confront him and ask about it. See if he could stop doing that. Or perhaps try to find someone else to work with or move to so your not near him. If it bothers you so much talk to your boss and see what you could work out.

Or beat him up..

He's totally hitting on you dude. And he's not cracking his neck, he's gesturing you to the mens room. It's a hobbit thing.

do like me and get a night job, i am here all alone.