Random Occuring Boner. This usually happens when a hot ass girl walks by you in the middle of class, you look at her, and POOF. Instant boner and instant embarrassment. Congratulations my friend, you have a ROB.
Tyler: "Dude, you need to get your ROB under control."
Grant: "Ahhhh man, she's so hot though. Oh shit, look away!"
Tyler: "That was disgusting as fuck, man."