'Keint' is a noun. It is a variation of the word 'cunt'. Other such spellings include: kunt, kant. The 'c' has been replaced with a 'k' to emphasise the 'k' sound.
Keint is an insult directly spoken by a Lad

Its pronounced how its spelt.

A casual invitation / threat used by an individual that is not afraid of fucking someone up.

a keen cunt. Term of endearment used in Australia. Derogatory term everywhere else in the word.