Abbreviated from "Well-deserved-boner," a WDB is the inverse of a no reason boner (or NRB.) It is an erection induced by a sexually exciting occurrence and/or something excessively masculine (often warranting a broner.) It has a definite motive and it stands tall with pride.
A: Dude, I tots just got a major NRB from Babe McTittypants over there.
B: That's no NRB, you have a WDB on account of her remarkably toned body and astonishing rack.
A: Did you watch the game last night?
B: OF COURSE! When Kobe buried that ninth three-pointer, I instantly had a WDB, and Fisher's winning shot at the clock nearly made me squirt.