The fun of your children using what you say against you.
We have a time-out corner in our home and when a house rule is broken, the person is sent to the corner and they need to apologize before they can come back out. If we ask something of Ariana and she doesn't reply or comply, she is given a warning, "I need to you pick up your toys please. If you do not start picking up toys by the count of 4, then you will go into the corner." That type of thing. Well, she knows how to push it and usually we end up at 3 going into 4 before she makes her move.
Lately, however she has been saying that to us. If we can't get to her request for whatever soon enough, she says, "Mom, I'm going to count to 4 and then you will go in the corner, alright?"