slang To best someone in a spectacular fashion and/or in a way that is humiliating to them. In basketball, to "dunk on" a defender is to perform a slam dunk over them, a move often considered humiliating to the defender. The phrase is commonly used in a passive construction ("(one) got dunked on"). Here's the part of the debate where she really dunks on him by completely destroying his argument. You can't just tweet at this person and make fun of their opinion. If you really want to dunk on them, you have to correct their horrible grammar too.