Jennifer Lopez is married to Ben Affleck -- and wants all the other ladies who still might have eyes for him to know it ... evidenced in how she barked at some onlookers Sunday.

The couple was out on the town in L.A. this weekend, and before Monday rolled around -- they were leaving dinner at The Ivy together ... with BA playing the gentleman for his wife and opening the car door for her, while going around the other side once she was in.

Right then and there, though, a group of women in another car driving by happened to see Ben as he was coming around to his door -- and they did a good old-fashioned hollah!

Check it out ... as soon as JLo heard 'em cat-calling at her hubby, she let 'em know how she felt about it right on the spot -- telling the ladies to "back up, bitch!" ... and in emphatic terms.

Ya gotta see the video, because J Lo's feisty clap-back is classic Jenny from the Block -- although, it's unclear if the women on the other end heard her. One person who certainly did hear her jab was Ben himself ... so he definitely knows he's hers and hers alone.