(for both, in british) Apologies original gangster, the one known as little thomas has ordered you to get bun. If you fail by the end of the week, you will get bun.
The boundaries of what a burger bun can hold before everything inside starts falling out, sliding off, or straight-up exploding. Cross the bun-daries, and you're wearing your lunch.
"I took one bite and the whole thing slid out the back. Bun-daries were not meant to be crossed."