I am so sorry for not having more detail and I only read this a short time ago. The story starts pre-Stanford. Sam and Dean go out to celebrate Sam's high school graduation. The get very drunk, pick up girls and have sex in the back of the Impala (not with each other). At some point John comes back to the room, Sam throws up on his boots and Dean (who doesn't realize that he's talking out loud) thinks John should be able to get laid with the awesome boots that he's wearing (or something like that). Turns out the girls were succubi (or some other evil) and John was hunting them.

the next morning John makes them eat greasy diner food and do some sort of training (and maybe wash the Impala).

Thanks for any help!!