to be the third guy to have unprotected sex with a chick in a short period of time. High risk of STD's since there's 2 guys and the girl's juices floating about. worse than sloppy seconds,but better than floppy fourths
Joe likes messing with the cheap prostitutes that don't like condoms towards the end of the night and usually ends up with dirty thirds.
When someone "hooks" up with someone after two of his friends have hooked up with them prior to said hook up. The term becomes appropriate after a situation where the term Sloppy seconds suffices. Coined by Bryce aka Gunky.
That girl is you're dirty thirds.
"Dude that girl's so easy. You could totally tap that."
"Wait dude, didn't Plowman and Trash can hook up with her?"
"Yeah, but dude she's so easy."
"Na man,I don't want their dirty thirds."