A game, similar to a sword fight, where each duelist wields a highlighter and tries to mark on their opponent. Usually, one should try to avoid being marked on by trying to swipe at their opponent's armed hand and block their attack. It gets messy.
Becca: Dude, why do you have highlighter all over your arms and face??
Mac: I just got in a highlighter war with my girlfriend!!
Becca: Highlighter war?? what's that??
Mac: Look it up on Urban Dictionary, woman!!