schoolboner
An erection that occurs during class as a result of either daydreaming or seeing a hot girl, usually experienced by adolescents and preteens.
James: "Damn, that girl over there has a nice ass."
Bryan: "Yeah, I just popped a schoolboner when she bent over to pick up her pencil."
Bryan: "Yeah, I just popped a schoolboner when she bent over to pick up her pencil."