Maybe it's not the best joke, but the fact that Hawkeye's joking about Dahlia and Radar at all, when he was so serious and tense the one time they really talked about it -- well. Radar's heart lightens, hearing that. A half-conscious worry that'd been gnawing at him for months settles down a bit.

Maybe it really will be okay.

"Yeah, yeah, okay," he laughs. "I'll see you around! Merry Christmastide! -- Or... yeah. You know."

And off he goes before any huffing or puffing can commence.