Jack doesn't have to ask twice but even though Spike's eager to get a good meal in and maybe engage in some blood play he paces himself. Grinning wildly with blood slicked lips he tugs Jack's trousers open and slides his hand inside to roughly grab and squeeze, eyes all the while locked on Jack to see every nuance of reaction he's got in him.
"Pervert."
Not that he's complaining at all. With a growl he dives in, digging his teeth into the junction of Jack's neck and shoulder. It's deep, not some little love bite at all, enough to spill plenty of blood, maybe even too much unless they get a free play through the magic of dreams.