Of all the damn things.
Taking Sammy on a hunt was still relatively new, but this was supposed to be a cake walk – straight up haunting, salt and burn. The hunt itself was mostly uneventful. Except for the part where the ghost exploded and showered the Winchesters in ectoplasm. Honest to God ectoplasm like in that dumb Ghostbusters movie.
It was kind of a race to see who could strip the fastest once they reached the motel – the stench was that bad. John sent Sam to the shower first because though they'd all been splattered, Sam had to deal with all that goop in his hair. It was a dejected, angry and somewhat mortified Sam who came out of the bathroom to announce that he couldn't get it out.
It was tempting…more than tempting to just decide to shave the kid's head. It would be so easy, and it was the perfect excuse for John to win the fight against Sam and his hair. But, Sam had some hard to explain bruises that were nicely hidden by his too-long tresses, so John had to get the goop out.
Ice didn't freeze it out. Egg whites didn't slide it out. Peanut butter didn't…John wasn't sure how peanut butter was supposed to help exactly. Lemon juice, mayonnaise, chocolate – none of it worked. John was at the end of his rope, and it was clear to see Sam was ready to opt for the "shave my head and be home schooled" option as well.
Then Dean arrived with a can of WD-40. To everyone's relief it cut through the ectoplasm and left Sam with a lustrous head of hair. Dean teased Sam endlessly about his silky mane and WD-40 became a permanent part of their field kit.