It sounds ridiculous, and he knows it. Worse: it makes him look ridiculous, and, regardless of how long they spent in the theatre business, no-one can truthfully say that they ever enjoy that feeling. Besides which, he has no idea what to say. "Please stop acting; you're making me uncomfortable," isn't going to win any awards. But he is uncomfortable, which makes Jack uncomfortable. Maybe that's the point.
Sloane is outlining something devious and borderline-crazy again, and Ron leans forward, his hand sliding down to rest on the small of Victor's back.
A thin grimace of distaste flits across Jack's face at the familiarity.