to remove someone/something from a list, such as a high-score list in video games. the slang form is when one graffiti artist crosses the name of another competing artist off of a wall. in slang, it is not uncommon for the term to also be used in situations other than spraypainting.
"who won the mc battle?" "the dude with the braids, he crossed all'them other fools out!"
"pass me that ps2 controller, I'm about to cross you out!...and get me a soda bitch"