Heiney, please?

I was walking behind Harper as she went up the stairs tonight (she... easily distracted and I... always impatient), so I was tapping her "behind/heiney" (my choice of words!) with my iPad to keep her on track.  She turns around says "Don't play with my butt!".  Despite my reaction, what I SAID was "EXCUSE ME??" and she immediately responds with "Bottom".  "Don't play with  my bottom, Mommy!"  I seriously need to walk around with a video camera mounted to my forehead these days...  I couldn't make this stuff up if I tried...