When a guy looks at someone else who is SOOOooo ugly or something that is epicly disturbing that their penis goes inside their body and comes out their butthole.
Dude, I had to go to the hospital yesterday because I saw this girl that gave me a Backwards Boner. The doctors were so disturbed it gave them Backwards Boners.
by IAmSoAwesomeSauce February 26, 2011
Where you are engaging in sex and you still have your whity tightys on, but you have to go poop really bad so you shit in your pants therefore looking like you have a "backward boner"
i was fuckin jenny last night but before that i had mexican so i shit my pants and got a "backward boner"
by James, Schwieger April 25, 2007