The riffs during a scene involving runaway truck rigs on a hill in Riding With Death, non-stop buttsex double-entendres that get more blatant and dirtier with each riff...culminating in one of the Bots' crack about "...and now, I'll be nudging yer sweet honey pot...", which leads Mike to put the kibosh on the whole thing.
Which of course, leads to this:
Mike: "Drained and satisfied, I'm tracin' lazy circles on yer' supercab now..."
The writers oftentimes say things like "You can get away saying certain things with a puppet that you couldn't with a person". Notably Crow's "I wanna decide who lives and who dies!" line from Santa Claus Conquers the Martians.
Too many to list individually, but they tried to get away with as many innuendos and double entendres in each episode as possible. Kevin Murphy is on record saying that basically the writers wanted both kids and adults to laugh at the same jokes, but for different reasons.
In The Movie (riffing This Island Earth), when Tom Servo blocks the hull breach with his hoverskirt, he starts giggling uncontrollably as the vacuum of space sucks at him from underneath, declaring, "I'm experiencing a sensation altogether new to me and frankly, I love it!" When Mike removes him, he growls, "Aw, darn!"