Yeah, Jack's starting to understand it, intellectually, but it's possibly something he's never actually going to get in his gut.
"Well, good for him! In public, too. Not that I ever really thought inhibitions were a problem for him!"
Demonstrating his own lack of inhibitions by sliding his hands lower to grope Ianto's ass - under the water, but still very much out in the open where anyone passing by on the nearby shore could see.