In this fun phrase the hot dog represents a penis and the hallway represents the enormous vagina. Usually due to the fact that the woman has had many many sexual partners which has stretched the vagina walls to the size of a "hallway".
Short for "It was likethrowing a hotdog down a hallway", this euphemism refers to what having sex with a really slutty girl might feel like. In essence, her previous activities have left her so loose that when you get in her, you can barely feel a thing.