What episode does this joke happen in?

I only catch incidental glances of this show when there's a rerun on; but after Clark Gregg's appearances in the various Marvel movies, I began to give it a shot.

There was one really funny moment where Christine insults his character (something along the lines of "OH YEAH?! Well back then, you had hair!" etc.) leading him to let loose one of the girliest squeaks I've ever heard and goes to cover his head up. Does anyone remember the episode? I've looked through the synopses for all of them seeing if any plot jumps out at me; but none of them do. I'd love to see that moment again.