Insane!Kai's Badass Boast from "Wake the Dead" is darkly hilarious once he gets to the end of it:
Kai:(crazed) I've killed mothers with their babies. I've killed great philosophers, proud young warriors, and revolutionaries. I've killed the evil, the good, the intelligent, the weak, and the beautiful. I have done this in the service of His Divine Shadow and his predecessors, and apparently the fun never ends!
Dr. Kazan: Your home will be the entire universe, aboard the Lexx, with me at your side! We'll be the crew, you and me! Be bold, Zev, don't compromise yourself with sentiment! Together we can own the universe! You know this is what you want! You are one of the chosen, we both are! Seize your fate!
Zev: ...Can't we just have sex instead?
Zev: What kind of robot are you?
790: I am a robot that wants to live in your underpants.
790's verdict on Stan when performing a medical analysis of him: "There does not appear to be anything wrong with him, aside from being utterly repulsive in every way."
Mantrid's gurning facial expressions when he's taunting Brizon in the episode of the same name have to be seen to be believed.
The childish insult-fest between the two of them is also a ridiculously amusing moment in an otherwise dark episode.
Stan:(regarding Kai) He was alive dead for two thousand years, but this time he was dead dead! Really!
Bog: Two thousand? That's a lot of birthday p-p-parties.
Stan getting the Lexx to call him by an assortment of ridiculous titles in "Giga Shadow".
Stan: Lexx, when you eat, can you separate out the yummy stuff from the nasty indigestible bits?
Lexx: Yes, Stanley the Perfect, the mighty and terrible champion of the oppressed.
Stan: And - unjustly maligned majestical being!
Lexx: And unjustly maligned majestical being.
Cranked up when Stan realizes the third-person aggrandizing is becoming more of a hassle than it's worth, and (accidentally) is now:
Lexx: As you command Stan, Stan, only Stan.
790 on distress signals: "They only lead to trouble, so I always ignore them."
"SLUT GERMS! SLUT GERMS!"
In Super Nova, a horribly injured Stan stumbles into one of the Brunnen-G's memory recorders, which causes him to relive the memory of the person who he was touching. The Time Prophet uses this to relay a message to him while the confused miner is talking to her because she's giving information to a guy who won't exist for another several thousand years. What's hilarious is the fact that Stanley forgets a detail and walks back, and the Prophet foresaw his blunder and shouted the detail at him.