A prank The rule is to eat two slices of white bread under two minutes without drinking anything, which is near impossible as it dries your mouth very quickly.
A less painful variant of the (in)famous cinnamon challenge.
"Have you heard of the bread challenge?"
"No, what's that?"
"Here are two slices of white bread, let's see if you can eat them in under two minutes."
"All right, let's do this"