At one of the parties I think it was the second round I made the comment (not thinking) "You look just like my grandma" 2 seconds after I meet her, because I was caught off guard that they looked so alike. After I said it I felt terrible and tried to explain that she does (not kindding) look just like my grandma when she was her age, they even have the same name (again I'm not kidding). Needless to say she was not happy and not as sweet as Grandma, which is great because that was one of my least favorite houses.
It makes for a funny workshop story though when we go over stuff NOT to say! (i.e. think before you blurt out something stupid)