Dirt Biking is the act of having sex with a woman on all fours. While in the act, the male slips his thumb into her anus and then makes motorcyle sounds while pumping the "throttle". The time that elapses from insertion of thumb until the time you get thrown off is to be compared amung buddies.

Used to describe (generally female) imagery that's suggestive, but in a PG-13 sense rather than an R or above sense.

When someone has terrible diarrhea and sprays shit up the back the toilet bowl/tank.