The Mary-Kate Olsen/Spencer Pratt war is officially on!

After an opening salvo on The Late Show with David Letterman, M-K revealed she used to go to high school with The Hills star villain.

"He used to play on the soccer team. " M-K confided on national TV to Dave while promo-ing new indie flick The Wackiness.

 "He would walk off the field."

Pratt fired back.  He calls the pint-sized thesp "a troll."

"I forgive her, though. She's had to go through life as the less cute twin, which must be tough."

Olsen also described Pratt as "wormy."

Hey, guys - calm down it's free PR for both.

Now go out and start a rumble with surfers or something more exciting.