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1.
Heard it on the daily show, and decided to come up with a definition for it. A dirty toothbrush is when a man has anal sex with his partner and then takes his penis and rubs it on his partners teeth.
Elliot Spitzer paid for a dirty toothbrush.
by Yatin Shastri April 29, 2008
 
2.
A dirty toothbrush is when a woman shits on her sex partners dick and he puts it in her mouth and rubs it just on her teeth.
lisa got a dirty toothbrush from chuck
by urbansexman August 22, 2009