Late seasons. Dean catches Cas masturbating in the impala one night bc he put a motion detector in there bc he was tired of people running off in his car. Sees stickiness. Chokes out "did you- did you cum inside her?!’ gets embarrassed. When Cas starts to answer he says “I don’t wanna know. Just – just clean her up and get out.”
Gets brainworms about it. Keeps noticing Cas’s life movements of sliding his fingers down the back of his cell phone before picking it up, licking cream off the stirrer, handling the leather shoulder bag full of case notes that sam hands off to him with care and affection and going crazy thinking about how he might have done all that to the impala. Asks 1 (one) burning question of why several days later at a diner while sam is in the bathroom and then castiel keeps going on about how he goes about it (kissing first, he is Making Love) and how the leather feels and how cared for and safe he feels inside her. It started when he was ‘human’, he came to understand her as a place of safety (and vulnerability) no matter the elements, and he slept in her once and started kissing her and “our relationship progressed from there”
“relationship – wh- she’s just a car!”
“[cas frown] you really think so?”
“I- no, obviously, she’s- urgh, whatever!! Why don’t you do that freaky shit to your own ride?”
“Dean. Be serious,” He sounds like Dean had just compared a supermodel to a slug. Although - knowing Cas’s certified freak status, he might be more into the latter. No amount of hysterical thought jumping can save him from hearing: “While the Lincoln has its strengths, you must agree that Baby far eclipses it in erotic potential. The leather alone-”
“Oh god shut up shut up shut up!”
He sees motion activate several other nights and has to jerk off about it, hard, almost painful in self punishment for getting infected with Cas’s freak shit. Eventually he decides to confront Cas again. Or maybe fuck him. He’s not sure. He gets to the door of the rocking impala, flashlight at the ready, swings it wide and comes across Eileen’s shocked face and naked body, where she’d been rutting into the edge of the seat.
“I can explain,” She says immediately, after Dean claps a hand over his eyes and groans in horror. “Dean, listen, I’m not usually like this, it’s just, the leather…”
“JUST WASH HER OFF AND STOP EXPLAINING.”
Dean declares the next morning that he will be keeping all sets of impala keys on his person from now on. Sam is nonplussed and complains about it: “What the hell? Why? It’s the family car.”
“I don’t know, Sam, maybe someone in this room would like to bring Sam in on what’s been happening in the family car.”
“It’s fine,” Eileen says, at the same time as Castiel’s “I don’t think there’s any need for that.” And then they look at each other shrewdly. Eileen signs something to Cas too fast for Dean to fully interpret, but he thinks he sees the word “leather” in there. Cas nods back and Eileen grins too widely and Dean buries his head in his hands.
