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3.
When your erection is only semi, it does not go all the way. This is actually more embaressing than a true boner because people think you 'cannot get it up'
HAHHAHAHA LOOK PHIL HAS A SEMI BONER OVER CHARLOTTE!
ITS PROBABLY OVER JOHNNY CAUSE ONLY HOMOS GET SEMI BONERS!
by chloerose444 August 14, 2008
 
1.
When ones penis is no longer erect, possibly either after blowing ones load, or just losing an erection. A semi-boner is often used for playfully slapping ones friends in the face while they sleep for a hilariously good time.
To try and piss my friend off, I got a semi-boner and helicoptered it around in his face.
by BLICK12 April 23, 2006
 
2.
A semi-boner is when a man's penis is no longer erect after blowing his load or just becoming aroused.
Some guys get a semi-boner to playfuly slap each other in the face with it.
by Tiea August 04, 2008