It's in the context of a French rap song "Nique La Police" - "La justice nique sa mère, le dernier juge que j'ai vu avait plus de vice que le dealer de ma rue". I can't find out what "niquer" exactly means by itself either - WR only gives a noun form "nique". I'm mainly curious because I don't know why it's "sa" and not "ta". I have this feeling this song is somehow related to N.W.A's (in)famous "Fuck tha' police" single, but anyway, I have wide musical tastes. Forgive me.