Teee-heeee Julie! Sometimes the only thing to do in this situation is laugh.
I was quite embarassed earlier this year when my three year old decided he wanted to play "peekaboo" when I was busy dropping his big brother off at school in the morning. I was standing with another new mum and we were making polite chit-chat, all was peaceful and well with the world.
Suddenly and without warning, Master 3 lifted up my skirt waist height, displaying my purple cottontail 'mummy' undies to the world and simultaneously yelled excitedly "PEEKABOO MUMMY!" at the top of his voice, this gesture thereby guaranteeing even more attention from the entire Kindy school community as parent's heads turned toward the action of me trying to wrestle him back out from under there.
It certainly made for a memorable introduction, I can tell you!
[In revenge, I took a series of "bath" photos for use in the future.........]