"I don't know, General, the more I think about it, the more you look like you'd be pretty easy to me." Fives absolutely knows Rex would progress from discreet jabbing to just flat out smacking him upside the head and possibly dragging him away while shouting apologies for his unacceptable behavior for this particular transgression, and finds he absolutely does not care as he grins. He's a civilian now, what's the worst that can happen?