And that's when I made this SHOCKING DISCOVERY!
Dean picks up the Leather Jacket from John's abandoned motel room! Meaning, that before the pilot, John was actually in possession of it...
As we know, Dean gets covered in mud and they check into a nearby motel for him to get cleaned-up. They walk in and see this:
See that wicker shelf beside the sink? See the clothes piled on top of it? and the clothes piled in the corner of the room?
How about from this angle, as Dean tries to tell us that he doesn't like chick-flick moments:
Just a pile of clothes right?
But when Dean comes out of the bathroom after his shower, he immediately reaches for that pile of clothes and low and behold, the Leather Jacket is on the very top:
That's right! John not only left his Journal behind for the boys to find - he also left the Leather Jacket of Awesomeness.
Now, you could argue that Dean could have brought in clothes from his car, including the Leather Jacket, and they just didn't show it on screen...but, after he tells Sam no chick-flick moments, he totally just turns and disappears into the bathroom...
My theory is that Dean just picked a change out clothes out of the ones that John had left in the room (there were a lot to choose from). John and Dean are pretty much the same size - actually, out of the two of them, John is a little bit bigger (at this point), and I was remarking to my friend before Dean fell in the water that I really liked the Chocolate Utility Coat he was wearing because it was just a little too big for him and made him look small and cute. I think Dean and John frequently wore each others clothes when they traveled together, since there wasn't as big a size difference as between Dean and Sam (who tend to keep their wardrobe separate).
Which would explain why in After School Special, we see Dean wearing the Leather Jacket while John is out of town, yet John has it to abandon for Dean to find in the Pilot.
Or, you know, you could just go with the "we don't see Dean get his clothes from the car" theory, and leave it at that...but personally, I think I just made a whole bunch of "John gives Dean the Leather Jacket" fics into AUs. ETA: Just to be clear - I do know the jacket originally belonged to John, I'm just talking about when it was that it came to be in Dean's possession permanently.
And yes...I realize how absolutely geeky this obsession with the Supernatural wardrobe is...but goddamn it, it makes me oddly happy. (If it makes you oddly happy too, check out my "If Clothes Could Talk" post...I'm partway through posting S3 clothes.)
ETA (months later): I always assumed the leather jacket that John was wearing in Something Wicked (1x18) was THE Leather Jacket, but it's not! Check it out: Different buttons, different seams, different collar:
Of course, Dean says in Dream A Little Dream of Me (3x10) that the jacket used to belong to his father, so that's not in dispute.