Don't know if this applies to your situation because our children were all boys, but here goes:
One of our boys went through a brief phase where he'd use table manners like a dog. Throughout his life this son has been an expert at pushing my buttons, and, goodness, did it push one of my buttons when I looked up and saw him lapping up food from his plate like a dog! Somehow my wife was oblivious to it, but at first I was thinking along the lines of "If he's behaving this way at home, he's going to behave this way elsewhere and people are going to think he's weird."
Well, after a few go-arounds where I imposed consequences for the behavior I finally started listening to my wife. She said our son was doing it just to annoy me. So, I made a few phone calls to adults who had eaten with my son away from our home. They all complimented me on what nice table manners our son had. (And, indeed, I noticed that our son always used good manners when we had dinner guests.) So then I decided to just stop getting upset, and when he was no longer getting me upset, over a few weeks time he stopped acting that way.
Just before the end, though, I do have to admit one instance of provocative behavior on my own part. One night when it was just our own family at the table, when our son was finished eating and started licking his own plate, I didn't say a word... but when he looked up at me for a reaction, I picked up my own plate and gave it a single lick. You'd have thought I committed a grave sin! "Dad! You can't do THAT at the table!" I just winked at him and said if it was OK for him, maybe I should start eating like that, too. He laughed and laughed - and I think only did it a time or two after that.
Anyway, it turned out to not be a long term problem, and he has grown up to be a nice guy with good manners.