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The result of someone who is turned on by a mentally handicapped person causing a boner, based on the combination of the words "retard" and "hardon."
"I accidentally clicked on some retard porn and I was surprised when I got a total retardon!"
by The Urban Queen Again August 22, 2013
A confused, erect penis that is held at a 45 degree angle.
The guy I was hooking up with had a retard-on, so I didn't know if i should've continued
by Yuri Hoshino March 05, 2005