Sorry

[Jim Tressel]

I stumbled across this tonight at work, don't ask how.  But here's one definition of "Dirt Bike" courtesy of urbandictionary.com:

2.     dirt bike   

A sexual act in which a couple gorges on spicy Mexican foot in the evening in preparation for sex later that night. Later in the night, the couple engage in sex doggy style and the woman develops uncontrollable, blow out diarrhea. At this point, the man grabs her arms, pulls them back behind her, and revs her like a dirt while she sprays feces all over the both of them (much like revving a dirt bike stuck in the mud)!

[Arctic]

Why

[Hawkes]

JT is there something you want to tell us?

[Reddawn]

poop is a natural lubricant

[Bleezy]

I would imagine that dining on a Spicy Mexican Foot would make it come out the other end.