"They hated each other in canon, how can you possibly ship them??"
You wanna talk canon? Alright let's talk canon.
Just the looks these two give eachother should be enough to rest my case.
Bobby licking his lips when looking at Crowley.
Crowley looking at Bobby while he walks around him, following Bobby with his eyes, just YEARNING for that man.
Crowley not wanting to let Bobbys soul go from hell and looking with HEARTS in his eyes at the sky where Bobbys soul is floating.
But there's more than the looks of course.
Crowley healing Bobbys legs even though he didn't have to and feeling awkward when Bobby thanked him for it.
Bobby calling Crowley pretty.
Oh and the banter, i love the banter.
"Bite me." - "if that's your thing."
"Let me get this straight. We just saved the sodding world together and you're too good to drink with me?" - "Obviously. I doubt that you have my brand." - "What's your poison, your highness?"
Bobby turning the lights off and revealing a white devilstrap on the floor where Crowley stands.
Crowley: "I hope thats paint."
I could list more things like this, but I think i already got my point across.
But let's not forget the most obvious reason:
Bobby shoved his tongue in Crowleys mouth just because he could so that counts as heavily making out. Crowley seemed to be into that though.