This term refers to a type of self mutilation performed by some crazy males. The man will slice the underside of his penis in half, starting right below the pee hole and ending at the start of his testicles. When the penis heals it looks just like a hot dog bun.
Phil was going to get some oral sex until Suzy saw his hot dog bun. That freaky looking thing scared her off.
Hot dog bun gun man: you are not worthy
Bill: nooooooooooooooooooooooooooooooooOoOoooOoOo i Want a hot dog bun shot in my mouth with a gun
Hot dog bun gun man: next
Hot dog bun gun man: you are worthy
Dave: LEZZZZZZZZZZZZZZZZGOOOOOOOOOOOOOOOOOOOOOO this is my dream, i love getting hot dog buns shot in my mouth.