In the episode where the family goes skiing Marge is sitting on the chair with her two legs up on an ottoman, a clock falls on her right leg. Yet when she goes to grab her leg, she grabs the left leg.
So why is this slip-up called wrong foot? All you do is talk about how the clock landed on her leg and she grabbed the wrong leg(which she didn't buy the way) and that she hurt her leg. Why call it wrong foot? And no she didn't grab the wrong leg. She grabbed the leg it fell on.