The Season 1 episode "Tangled Web" features several brazenly sexist remarks against Kimiko (mostly from Omi) stating how women are both physically and mentally weak and require men to help them do everything except for cooking. Had the episode not involved Kimiko defying the "damsel in distress" stereotype, the episode might have been banned at worst or toned down due to Executive Meddling at best.
From the episode "Bird of Paradise":
Jack Spicer: If anybody deserves the Bird, it's me!
Likewise, from "Year of the Green Monkey":
Omi: Now, if you all will kindly look away, I feel the urge to scratch in a place that I have never scratched before!
In "The Demon Seed," Master Fung, Dojo, Kimiko, and Clay get turned into plants. While Raimundo and Omi are tending to them, Omi grabs some kind of apple from Clay's belt area and eats it, causing the horrified cowboy to protest, "Be careful what you go pluckin' there, partner!"
In "Treasure of the Blind Swordsman", the Blind Seer guarding it has a tendency to mishear things.
Blind Seer: (captured) Hold on! Where are you taking me? I have to use the bathroom!
Wuya: (To Jack) What about the treasure chest?
Blind Seer: What? That's disgusting!! (Beat) ...you talking to me?
Dudebot in "The Deep Freeze" basically commits suicide.
In the same episode Omi holds up a carrot asking if anyone wants to make a snowman - which makes sense in context, but due to how Omi is holding it, the grin and his small figure which makes the carrot look huge in comparison the image itself is rather questionable.
This exchange in The New Order:
Jack: Well, I've got something that you don't!
Chase: *smirking* Very small hands?
Jack: *annoyed* No.
Kimiko's "Fire!" Invocation can look a little questionable if you don't notice that she's wearing tights under her somewhat- Qipao-styled Xiaolin robe. Given that they are slightly lighter than she is, you might miss them.
In "Something Jermaine" when Omi screws up Jermaine's retrieval of the Shen Gong Wu, Jermaine asks Omi if he's tripping. Either the writers weren't aware that "tripping" is slang for being under the influence of the questionable drug LSD, or the censors didn't. However, it can be neither, as "tripping" (often spelled and pronounced as "trippin'") has been (and still is) used as street slang meaning "to be crazy" or "to be kidding around."
The "Woozy Shooter" is a Shen-Gon-Wu that emits a gas that causes people to act silly and experience bizarre hallucinations - somewhat similar to the effects of psychedelic drugs (however, the episode arguably portrays the drug experience negatively, as it used against the Xiaolin monks to hinder them during the episode - so this is likely why it wasn't regarded as promoting recreational drug use). Heck, its shape is similar to either a hookah or a bong.
In "Wu Got The Power" after Jack says something stupid, Hannibal Roy Bean speculates he must have an extra chromosome, a subtle way of implying Down's Syndrome or mental retardation in general.
In Time and Time Again part 1 We see where overlord jack keeps the other major villains prisoner. Wuya is hanging on the wall dressed up like a cheerleader, and Chase Young is restrained while...a machine spreads butter on his abdomen...
It's yellow paint. Yellow belly is an insult meaning coward