Gladio rolls a shoulder into a shrug, playing it off easy. "Don't like 'em unless I'm with a total stranger. Pretty sure you'd tell me if you weren't clean. You're not the kind of guy to hide something like that." He doesn't know but he knows, thanks to the Bond. He bends his head down to press a kiss along John's inner thigh, then spreads both of his hands over those thighs so he could hold them in place while he met John's eyes.

Then, with a little bit of a proud smirk, he takes the head into his mouth... and proceeds to deep throat John in one long bob of his head down until his lips brush hair. If he needs to prove himself more, he even leaves himself there in place for a long moment before pulling back, then flicking his tongue over the head. Smirk again.