look up any word, like sex:

1 definition by ivegothookworms

The phenomenon where the bottom bun of a burger mysteriously disappears faster than the top bun. The eater's thumbs are precariously placed on a postage-stamp sized "under-bun", while the top bun is still the same size as the burger.
Your thumbs are covered with ketchup because you've got a bad case of under-bun syndrome.
by ivegothookworms June 29, 2010