"Riding the minipad" simply means that a female is menstruating, or, rather, the female is on the rag.
Two examples:
1. (Regarding menstruation.) My girlfriend won't be any fun tonight, she is riding the minipad! Perhaps she will let me ejaculate in her mouth?

2. (Regarding fucking.) I fucked the devil out of your cousin. She'll be riding the minpad for a while, to soak up all my semen and prevent it from running down her leg. You KNEW that your cousin doesn't wear panties, right?
by Rook's Buddy May 10, 2010
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