Say Hi To Your Mom For Me

Line from "Back to the Future" 1985, Universal delivered by Biff to Marty McFly after Biff has wrecked the McFly family car, had it towed back to the McFly residence and denied responsibility for it.

Biff desired Marty's mother when he, Marty's mother (Lorraine) and Marty's father (George) all attended high school together and Lorraine choose George opposed to Biff.

Biff is still stinging from it some thirty years later and has no problem taunting Marty with an inappropriate and disrespectful comment that he still desires Marty's mother, a married woman.

A phrase implying that the person saying it "knows" your mother, but in the biblical sense; and that your mother is a woman of easy virtue. Interpretation depends on the context, of course. In the long tradition of putting down someone else's mother as a way of putting them down. Alternatively, just "say hi to your Mom."