A slang term for the anus. It can be used to denote the asshole or it can be used in a pejorative way when describing someone whose asshole you'd like to fuck. The person in question becomes the dirtbox in question thus reducing them to a fuckhole and nothing more.
An example might be "Wow, she's cute. That's a lovely little dirtbox there." That would usually be said in the exclusive company of men. It can also be used in a loving way by members of the gay community. An example might be "Hello Jeremy, I was thinking that maybe this evening we could have a quiet meal in that new Italian restaurant down by the river. Then I can take you home, rub your feet after a long day and then light some scented candles. Then we can make out and I can then lube up my tube and poke it right in your dirtbox. How does that sound?" It's a very versatile word.
An absolutely foolproof way to keep minors from viewing content deemed "too mature" for them to watch.
Billy: "So I was trying to watch some videos for an M rated game, and I ran into an age gate, so I put in my real birthday. SOMEHOW it managed to figure out that I am 12. CURSE YOU AGE GATE!!!"
Bill: "Fucking age gate! *quick scroll* THERE! I was born on January 1, 1904. Fuck you age gate."