When they try to lure the Evil Thing to them with a recording of its mating call. Just as it gets close to them, they press the wrong button and begin blaring hip-hop.
At one point Max has an extended sequence of brushing his teeth... before taking another bite of a cookie before even leaving the bathroom, making the entire scene pointless.
"A Creature Was Stirring": The end where the Krampus turns out to be a Christmas present brought by an SUV-limo riding Santa Claus.
"Poof de Fromage": Just the thought of alien leeches posing as cheese curls is one of those things that's funny because of how Jean-Louis (the alien posing as a French exchange student) takes it seriously.
The Answer Cut when Bobby asks what happened to the real Jean-Louis (since the boy known as "Jean-Louis" staying over his house is an alien posing as a human boy): The real Jean-Louis is tied up, stripped of his clothes, and left in the unclaimed baggage area at the airport.
Part two of that episode gives us this gem right after John, who was turned into a tick creature, was on the receiving end of a Groin Attack. The actual impact occurs off-screen, but the dialog makes it obvious what happened:
Nathan: Ooh! Right in the...
Lisa: In the what? Does he even still have any?
(John doubles over in pain)
Nathan: I'll take that as a yes.
Big Yellow dancing in "Mascot"
"Terrible Love": A rather darkly funny one: Stuart comforts Maggie — who just saw Brendon fall down the stairs after telling Cupid that she wanted him to leave her alone — and signals Cupid to shoot her with his love arrows. Maggie drops dead and wakes up a few minutes later, blissed out and in love with Stuart.
Cupid sarcastically whining, "Oh, no! Not a scene partner." when Maggie calls upon him to give Brendon another love arrow.
Ethan trying (and failing) at learning how to be a cowboy in time for his shootout with "Mad Dog" McCoy in "Coat Rack Cowboy."