Oz knows what makes Xander tick. He's observed many adolescent males. He is, technically, one himself. There's lust. Social pressure. Insecurity. Lust. A desire to appear cool. Hopes for the future poorly married to a work ethic designed to deliver same. More lust.
Sometimes Oz feels a little guilty that he has a reputation for cool. Pretty often, that faraway look in his eyes is because he's just thinking about The Sex.
Oz has basically had an erection since he was fourteen. Sometimes it eases, thanks to effective masturbation techniques and/or really complex calculus. But, mostly, he's been cock-fixated throughout. Three women and two men have happily assisted with this condition. Oz hopes Xander will be the next.
He has a thirteen-point plan to achieve this end. He's on point three (mysterious silence, occasional smiles of complicity) and is eagerly anticipating points seven through twelve (moving from occasional touches to deliberate caressing by way of oral and manual stimulation) before finally getting Xander Harris naked and begging the way he should be.
But one night, coming home from patrol, and with Oz at the point of entering onto point four, Xander suddenly takes a giant leap through the program structure and says, right in Oz's face, "Oz? You're thinking about sucking my dick, right now? Aren't you?"
This is more than unexpected; it's off the charts. Oz waits to see if the perfect answer comes to him. None occurs, so he goes for simple truth. "Yes. A lot."
Xander, in typical Harris fashion, backs right off. "Huh. Uh. I- Yeah. I just-" He's about to retreat and pretend that one bold moment never happened, with every fibre of his mostly-conventional soul.
Oz decides he needs to scrap the thirteen-point plan, and press home his point. There are such things as windows of opportunity, cliché though the phrase might be. "I think you'd enjoy it. I know I would. Want to?"
This is totally not the perfect atmosphere. Oz doesn't need soft lights and romantic music, but he does prefer relative privacy and an absence of possible vampire attacks. The backstreets of Sunnydale offer neither. But if he lets Xander go now, he suspects this won't ever be on offer again. This isn't an expected approach from Xander. He doesn't know how to deal with it, but his instincts are screaming not to turn down this offer. So he presses Xander into a semi-dark alley a block or so from the Bronze (Buffy came this way earlier; vamps are unlikely). Reaches up to bring Xander's head into line with his mouth. (Tall guys are tricky to seduce, but Oz has worked on this before.)
Good mouth. Oz has enjoyed watching it. Wide and generous, and Xander responds well to Oz's firm, determined rhythm. It's important not to let Xander think too much about this. He overthinks. Reacts and is then ashamed of his reactions; hides from his own self. Oz will not let that happen tonight.
So he goes for the instant attention-getter, and starts working on Xander's belt. They're pressed together close enough he's sure Xander's cock is into this, whatever Xander's second thoughts are doing.
It's awkward, jamming a hand down half-buttoned jeans, but it's always worth it. That moment when Oz first gets his hand round Xander's dick is… yeah. Even Oz doesn't need to think too much about this one as he automatically rearranges them both to get better purchase. Warm, soft-skinned, leaking at the tip already, and Xander's groaning in the back of his throat and pressing up into Oz's palm. No second thoughts coming any time soon.
Oz is getting off on doing this. Very much so. But he promised cock-sucking, and he likes to deliver. Transition will be tricky; too exposed for too long, and Xander might yet reconnect with the scared back-portion of his brain. (It's not that Oz would stop him leaving if he ever decided to. But it is that Oz would rather not make it simple for Xander to argue himself out of this.)
Reluctantly, Oz moves back a little, giving himself space to manoeuvre Xander fully out of jeans and underwear, at least down to the knees.
The alley's dark, but not so dark Oz can't see and appreciate Xander's desperately twitching dick. Very nice. Also very near the edge. Oz would rather take time to appreciate this, but he's also an adolescent man and he knows gonna-blow-any-second when it's right up in his face. So he does what he's intended all along, and gets his mouth round the slippery, straining head, grasping the shaft with one hand and cupping Xander's balls with the other. (An unnecessary refinement, the last, from Xander's point of view. Oz doubts he'll have time to appreciate the extra caress before he comes. But Oz is a connoisseur of sex smells these days. Every man's balls smell different. He wants to carry Xander away on his fingers, after this too-short encounter is over.)
Xander's gasping, hands trying to grasp Oz's short hair as his head bobs with his sucking. "Sorry, gonna- Can't-"
Oz doesn't want to break the moment, but he thinks Xander's a guy who needs reassurance, or this could end with needless embarrassment. So he disengages his mouth from its happy task, and says, "I want to swallow everything you got."
Which is the truth. Flooded with Xander's taste as he comes, Oz's senses are on fire. There's touch, but now with the wolf, smell and taste are magnified in Oz's sex brain. He could come just from this taste, if he wanted.
But this isn't the time. So he tidies up Xander, who's pretty much occupied just trying to cope with leaning. Looks him right in the eye, and kisses him hard, so Xander gets their tastes mingled. Oz is marking him for the future.
You won't forget this. You'll want this again.
For the second time that night, Xander shocks him. He kisses right back, and then flips so Oz is against the wall.
His voice is a little tense, but there's no doubt at all to be heard as Xander says, "Your turn."
Oz realises he probably doesn't need to think and plan on this any longer. And so he just feels.