Kaitoa means: Good job! Take that!
There a couple of idiomatic uses of kaitoa. The kupu Māori for “idiom” is “kīrehu which is derived from “kī” (saying) and “rehu” (dimly seen, obscure).
It can mean “serves you right” or “take that” as in today’s prompt, expressing satisfaction at another’s misfortune, but it can also mean “thank goodness” as in “kaitoa kua mutu” (thank goodness it’s over). In some cases, this is split into two words “kai toa!”.