Here are the banned phrases at our house:
1) "That's not fair." Or, any use of the word fair when used in comparison to what a sibling or parent is getting that they aren't.
2) "Actually..." This is usually followed by some smart alecky correction about how the parent is wrong and the kid is thus going to correct them in the middle of getting in trouble for something else. Basically, it's pointing out that they are right for no reason.
3) "One minute." This is said to me anytime I ask a kid to do something for me. I don't have "one minute" to wait for them to finish playing with Legos, or whatever, I need them to do what I've asked them to do for me right exactly now.
What words/phrases are banned at your house?