“You’d better watch your back when you go back uptown.”

That was the ugly threat snarled by the mother of killer Natavia Lowery to a shocked defense lawyer after Lowery’s trial for murdering “Realtor to the Stars” Linda Stein.

The frightening message set the lawyer and his co-counsel free yesterday, according to a source.

The threat was hurled by Lowery’s mother, Lottie, against lawyer Thomas Giovanni during a shoving match near a courthouse elevator Monday. Yesterday, Manhattan Supreme Court Justice Richard Carruthers called it “inappropriate and threatening.”