He knows Finn's just continuing with the teasing and flirting at this point, but still, Jim can't help respond to that last remark accordingly, even as his head remains ducked against Finn's shoulder.

"Oh, I get it. So I'm just some kind of test run, so you can get better at flirting with other people."

Too mean? Nah. Surely Finn will know he's just teasing him too.