Well, Farscape has given us plenty of hysterical moments, but my two favorites are from "The Flax" and "Won't Get Fooled Again". (That's right, I have a hard time choosing...)
The revelation of Stanz as the female of his species in "The Flax", and his plaintive cries of "I love you!" to D'Argo got howls of laughter from yours truly. And the sight of Rygel in a gimp mask, rising up to peek between John's legs in "Won't Get Fooled Again", nearly did me in - I was laughing so hard I had oxygen issues.
And speaking of "Won't Get Fooled Again", Lani Tupu is comedy gold throughout the entire thing, from his understated muttering of "Toto..." to his high-octave high-heeled scene towards the end of the ep...oh, my.