Another zinger is "You know we don't act like that, no matter what other children are doing!"
I've used that one as well!!!!
I have been known to announce to the offending parties: "WALK!"
I hauled a kid over to his neglectful grandmother a few months ago when he was climbing on a display of tomatoes and pretending to shoot my boys with a banana. She just looked at me and skulked off with the little monster.
My kids were appalled at both his and her behaviour.