Er... obviously it's in the trunk because that's where they keep all their sex toys. Just makes sense to keep it together right? Dean made that rule after Sam kept forgetting to pack the lube. Boy won't forget the dildos, but that lube. It's *ahem* slippery stuff.
It's in the trunk because one of 'em left it in his other pair of pants. Apparently, however, Dean is SO horny and the spot he's eyeing for the spontaneous buttfucking is SO perfect that he just can't wait for lubrication, damnit!
See, it's a little-known fact that Dean likes his guns so much he likes to use the oil for lube. But just for Sammy, because other people used to give him funny looks when he pulled it out for them. But Dean won't admit to stuff like that, so Sam always gets the oil out of the trunk because he luffles Dean so much. :-D
Page 1 of 2