crawled up your leg and bit your bollock

A term used when someone, usually male, is more pissed off than usual - if something crawled up your leg and bit your bollock you would quite understandably be pissed off.

Usually quite a subtle way to tell them they're acting annoyed, funny too.

Joe: " STFU DUDE!"
Jim: "Damn, what's crawled up your leg and bit your bollock ?"