A trend either worn by: a- celebrities such as LL Cool J back in the early 90's or Eminem, b- the thug or gangsterish crowd, c- people who ride bikes.
Situation: Adam had "one pant leg rolled up" accidentally. Melissa gives him an awkward look. He says, "Yes I'm gangsta!" She replies, "You know who else wears their pants that way?... People who ride bikes!"
Hysterical.
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 ?"