Accidental Innuendo: Xavier has a knack for this trope. For instance, in one episode, a woman tells Xavier her husband beats her because he loves her. Xavier responds "If that's love, I'm going to make some love to his mouth!"
Bizarro Episode: It might seem impossible considering how Mind Screw the show is even at its most normal, but "Damnesia Vu" and its Sequel Episode "Damnesia You" take the weirdness to a whole new level. It's hard to properly describe in words, but both forgo any kind of plot altogether and instead just having Xavier go through various doors into alternate universes, none of which make any sense at all, only to find himself back in the room where he started, with no explanation.
Crosses the Line Twice: In episode four, Xavier doesn't eat a baby. He eats seven, pulls out one of their skeletons, makes a herd of bloodhounds tear an eighth baby to shreds, turns in to a fetus, gets electrocuted, transforms into an egg, hatches, promises to put babies in a stranger's butt and sticks his tongue down her throat. It's even weirder than it sounds.
In the episode before that, a kid's father is blown up, but the explosion is brought to life and becomes one with the kid's father. It's a little creepy. Then the kid stabs the explosion to death with a knife to keep his promise to his mother not to be another Einstein, and it's surprisingly poignant. Then Xavier rips the explosion's heart out and eats it, and it's hilarious.
Heck, just the entire show really.
Love It or Hate It: You either love this show or think it's one of the dumbest things [adult swim] has ever put out. There's little room for a middle ground.
Nightmare Fuel: There's quite a bit throughout the series, though what really takes the cake is the ending of "Signs from Godrilla", where Xavier is eaten alive by a mob of people.
Uncanny Valley: The intentionally low-quality CGI makes everything seem like a bizarrely unconvincing imitation of reality, be it places, objects or people. Xavier might actually be the most normal-looking thing in the show. Part of the reason for the trippy feel it has (besides, y'know, everything else).