Any Advice?

I LOVE all our girls more than I can even put into words.  They bring me joy everyday, but there are times when they bring me....... not.so.much.joy.  Like today....(side note)
 our youngest is potty training, can I get a woot, woot?!?!?  Well, the girls were eating dinner and she just pinches our middle.  Out of the blue, for no reason! Makes me CUH-razy!  Here's our conversation:

"Did you pinch your sister?"
(shakes head yes)
"Why did you pinch your sister?"
"I's mad."
"Why were you mad?"
"I dunno"
"Children who are almost three know."
"I's mad.  I want ice cream."

WHAT?  You pinch your sister and you want ice cream???? SERIOUSLY?  I know what you're thinking... I gave in, but NO I DID NOT. No ice cream for you!  She just does random things like that and it drives me crazy!  She always admits to it which is helpful, but still makes me nuts.  We've done time-outs, consequences, etc.  but what do you do?  I know she's only almost 3, but I'm sure we are going to be called into the principal's office one day to pick up our "sweet little princess". 
So I ask... what would you do?  Any advice besides giving her to the sheriff?  :)

From our Brown Eyes to Yours,