What it means
A cheeky compliment for something outrageously good, especially a bit of football skill like a nutmeg, screamer, or silky pass. If it’s so smooth it feels unfair, it’s filthy. The joke is it sounds nasty, but it’s pure praise, the kind you shout when someone’s just embarrassed a defender and made it look easy.
Usage examples
"Did you see that nutmeg at five-a-side? Filthy. He sat the lad down, took two touches, then fizzed it top bins before anyone could blink."
"That bassline is absolutely filthy, turn it up."
"She pulled off a filthy trick on the half-pipe."
"That roulette in the box was filthy, sent two man for a hot dog and still had time to pick his corner."
"Nah, that little reverse pass was filthy. Didn't even look up, just opened them clean in half."
Where it comes from
Stretches filthy, normally meaning dirty, into a compliment: something so outrageously good it feels almost indecent, too good to be clean. The same wink as calling a great tune wicked or sick.