The fact that Sulu's attempt to prove his universe's existance had turned out to be a pretty good time for both of them made Sulu a little self-satisfied. He couldn't help it; he'd invited Ianto over to prove a point and in turn ended up having a good day out on the boardwalk, showing off to a kid from the 21st century.

"Yeah, well." Sulu scratched the back of his head briefly, "Uh, no problem. Glad the future's not boring, or whatever." The fact that he was trying (and failing) to play it cool was pretty obvious, all things considered, but he was (somehow) not trying to be cool at that moment.