Iris was unabashed and Len was impressed. Not quite enough to admit that he was, just yet, but definitely impressed. Not possessive, at least. If he'd detected any of that in their exchange he would have been heading toward the door already. He didn't have the patience for that kind of thing. Jealousy and insecurity. Mostly all he could perceive was very real affection between the two of them. Something he couldn't match but didn't intend to try to. The interest he had in Barry was purely attraction, not affection. At least it was easier to tell himself that. Rather than mull over the fact that he was also particularly pleased that the kid, somehow, actually believed in him.
It could have been uncomfortable, but he didn't detect anything like awkwardness when Barry seemed ready to pick up where they'd left off. He hadn't been expecting an audience, of course, but it wasn't in Leonard Snart to let something like an audience deter him from from something he wanted. And he certainly did want. The way Barry was biting his lip only made him focus in on him more.
He smirked and pushed away from the counter where he'd settled to let the two of them have their hello's, but with the OK's from both parties involved he wasn't going to put it off any longer so he moved back over to lean down and in.
"Shut up, Scarlet." Len slipped his hand around the back of Barry's neck just to reel him in. A quick up and down stroke of his thumb was the only pause before he kissed him. Not chaste, because it wasn't in Len to do anything that way, but even he didn't go straight for obscene on the first try.