I have watched it over and over and laugh just as hard each time. It is far and away my favorite episode, of any show ever aired! The writing is excellent, the timing is flawless, the laughs are non-stop from beginning to end.
It's hard to pick a favorite line, because there are too many candidates, but if push came to shove I'd have to say my personal favorite has to be when Gill says "I see Kitty has claws!" I will say this line to my husband every now and then, and it cracks him up completely each time!
The writing was extremely clever in this one. However, if worked especially well because Patrick Stewart's acting was exceptional and it was nice to see how well he could do comedy. Well worth seeing and quite interesting to see Frasier being a wicked tease!