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.
"Hey man, the other night I dirt biked her for 54 seconds. funny thing is, she never called me back".....
by Hazyredeyes August 14, 2009