At least Fabian knows what she's doing here when she puts on that voice. At least enough that he doesn't take offense at it, knowing that Mal is just engaging in the similar sort of banter Fabian started only a moment ago.

"There haven't been enough opportunities to do so!"

.. for better or worse, considering most of the time when Fabian is dancing, he's actually engaged in combat..

"I mean, we have only had one proper party, and I had to throw that one myself! When else am I going to dance here, huh? There has to be something to dance about in the first place!"