My 11 year old son quite calmly made this gesture earlier:
..and said "mom, what does this mean?"
For those not in the know, the gesture is called "The Shocker". It has sexual connotations - the accompanying rhymes are 'two in the coot, one in the boot' or 'two in the pink, one in the stink'.
Yeah, you get the picture.
So, I had to do my best to explain it to my son, who, after he realized what I was talking about, shuddered, gagged and said "that's gross".
I highly doubt he'll be saying the same thing 4 or 5 years from now....