"No say me Seth"

My husband is probably one of the most sarcastic people that I know, which is just one of the many reasons that I fell in love with him. That being said, I am not sure if sarcasim is all learned or if some of it is genetic, but Seth has definitely started demonstrating this behavior, and it is keeping us laughing. The other day we were all in the car, and it had been a LONG day. I had heard "Mommy, Mommy, Mommy, Mommy" one too many times, so I turned around and said, "I don't want to hear Mommy one more time tonight! I am not answering to it!" (I know, I am probably the worst mom) Payten, the sweetheart that she is, immediately gets quiet and says, "I'm sorry." Seth immediately responds with, "Then no say me Seth!" To translate: You can't call me Seth for the rest of the night if I can't call you Mommy." Needless to say, Jon and I started laughing. Only a two-year old can get away with talking back like that :-)

How can I stay mad at this sweet face for too long?