We sure have!
Considering Jack was mostly teetotal for several decades, the booze thing is something they don't actually have in common, although it's certainly not something he has a problem with. And it's certainly not something he's unfamiliar with when making love to someone who looks like Spike, since John pretty much spent his entire life half-cut.
He's very aware, however, that this is not John. It's Spike, finally Spike, and somewhere along the line this has progressed from being just another dream/fantasy about finally getting there with Spike to being aware that it is the first time. That this is the first time he's actually felt Spike grinding down against him like that and, boy, is that hot. It makes him groan and arch upwards, cock suddenly achingly hard, and he flings his head backwards out of the kiss because suddenly there's just not enough air and he needs to breathe to get through the jolt of lust that rushes through him. "Spike...!" he groans, hands still everywhere on Spike's back to make up for the break in kissing.