I was reading a book on F1 when I came across this quote:
"Understeer is when they hit the Armco with the front of the car; oversteer, on the other hand, is when they hit the Armco with the rear of the car." - Jock Clear, BAR-Honda
On top of it being funny, this explanation has got to be one of the simplest and easiest to understand. Granted, in order to find it funny, one would have to understand the difference between the two terms in advance.
Anyways, I just thought I'd share that with you...