A dirk is a cigarette. A dirk stain is the yellowing of the fingers due to the dirk smoke.
Katie: "ew man I need to quit smoking, these dirk stains are seriously gross!"
Jon: "cut up a raw potato and rub it on your fingers. I guarantee it'll take away your dirk stains"
The act of jerking off into an open joint then smoking you or your friend's semen
The last time I went gram staining was when I was with my dad
Crusty stains in incriminating locations
From the looks of the pajama stains I'd say all you've done this weekend is beat off and inhale cheetos.
A person who makes bad plays in proffessional card events.
That kid Kevin is such a stain.
A person that no one likes and extremely resembles a stain left by a poop.
The presence of perspiration soaking through one's shirt located under a fat man's breasts, much like that which occurs in the arm pit.
In a hot college basketball stadium:
Student 1: Whoa look at that guy's pit stains.
Student 2: Dude those aren't pit stains, they're tit stains.