An individual who jacks off in class...generally to his respective teacher. (Abbreviated SB)
1. A: DUDE that guy is totally jacking off in class!!!
B: What do you expect...he's an SB

2. A: What do Semen Boys do?
B: Jack off in class....duh
by The Revealer of the Truth February 9, 2010
Get the semen boy mug.