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1.
Happens after you clog a toilet with a serious dump. As the bowl overflows, there is one little floater that stays inside the bowl and rides around the rim as the water still swirls from the prior flush.
Dang, I just stopped up your toilet. At least you've got a rim rider cruising around to cheer you up!
by Fecaloctopus January 18, 2010
 
2.
A "Bed Event" where a man takes the hard "mushroom cap" of his penis and runs it across and around the rim of a girl's pukered anus but not to penetrate. Therefore rim riding has commensed.
"Girl! Tammus was a rim rider last night for about 20 minutes, it drove me nuts."
by dang chicago August 26, 2008
 
3.
1)A person who enjoys the pleasure of being anally invaded. (Also cockjockey)

2)A person who is not highly regarded in your opinion
1) Elton John

2)"Bob? hes a real rimrider"
by Dan November 15, 2003