slaan = (verb) to hit, strike
If you think somebody makes a really stupid or unfriendly remark you think isn’t fair, you can use either one of these expressions:
Waar slaat dat op?
What’s that got to do with it?
(Or: What did I do to deserve this?)
Dat slaat nergens op.
Come on, it’s got nothing to do with it
(Or: That’s unfair)
(stronger, more irritated:)
Waar slaat dat nou weer op?
What on earth has that got to do with it anyway?
(Or: you are talking nonsense)
(Used in a subclause, less irritated:)
Ik snap niet waar dat op slaat.
I don’t understand what that’s got to do with it.
(Or: I lost it completely)
And last but not least:
Dat slaat als een tang op een varken!
(lit: That hits as a pincer on a swine)
It makes no sense at all.