I revive this stale post because I need help from the native English speakers here to understand a piece of dialogue between Lois and Clark.

The exchange is the famous one at Lois' doorway, at the end of the date. From the transcript:

Lois: No, I mean a _really_ nice time. Maybe the best time I ever had. It wasn't the funniest. Or the wildest. or the --
Clark: Don't knock yourself out, Lois.


I just can't get it: what are they meaning? Is she trying to downplay how well the date went? Is he ironic?



Go I Know Not Whither and Fetch I Know Not What