Jackson doesn't expect it. When he says 'you'd've sucked at being a guy, Lydia', it's more to rile her up than anything else; no matter how much he loves her she still gets on his nerves. Even more so, now that she's pack and can easily sense all sorts of discomfort from him.
So yes, when she looks at herself in the mirror while brushing her soft copper hair and asks -sort of absently- what she would've been like as a boy, he resorts to empty venom. Because it's easy to.
And thus it comes to this, to her ultimate desire to prove him wrong in all and any ways she can think of. It comes down to her, standing in drag in the middle of his room, smirking all boyish at him.
The first thought that crosses his mind is: Lydia looks smashing in drag. But of course she does, Lydia is perfect, that's that and a fact of life (his wanting to make it any less true doesn't actually make it any less true). She hides her hair under a hat, binds her boobs and wears a loose shirt, and wears stylish boy jeans.
She looks like one of those teen idols from boy bands and stupid tv shows for girls sixteen and under.
It's unfair how hot it is, how delicious her ass looks covered by the rough cut denim, how good the illusion of short hair works for her. It shouldn't get him this hard, shouldn't make him pant in this desperate manner.
"Dude, are you gonna suck my dick? If not, close your mouth." Her voice sounds deeper than he's ever heard it, a little strained under the effort, sounds as though she'll wake up tomorrow with a sore throat. It's not a perfect pitch, but damn it's a good try.
The words, however, are what make him groan and kneel in front of her like an obedient puppy.
She unbuckles her belt, drags the zipper down and...
Takes out a prosthetic that's clearly attached to a strap-on. He whimpers at the sight and the sweet sweet smell of Lydia's wet arousal underneath silicone and leather.
He sucks, messy and as deep as he can, covering everything in his spit, choking himself until he feels he might puke. Lydia says, whispering roughly, "Like that, good boy. Get me wet and sloppy so I can fuck you."
If he doesn't come right then and there, it's because he craves to do so when she's finally sinking inside of him, tearing him up and muttering dirt into his ear.
It's so easy for them to get underneath the other's skin nowadays, he thinks, as Lydia pulls his hair and he whimpers. So easy.
And so they do, because even before werewolves they've always been itching to get underneath the other's skin, to be the pain that can't be chased away, the leftover tingling.
When he cries out Lydia's name, he can feel her satisfied smile resting against his slick back.