Profanity level depends on the era. Before 2014 words higher than "Bastard" were bleeped most of the time. By 2017, the entire channel became uncensored with uses of "Fuck", "Shit", "Asshole", "Bitch", etc. in every episode, mostly excessively.
Racial, sexual and homophobic slurs are used as well.
Retard was used by Bully Bill in some episodes.
In the episode of "The Test!" Jeffy writes FUCK THIS TEST but he erases later.
In "Brooklyn Guy's Early Christmas!" Brooklyn Guy angrily yells at Rose "NO! FUCK YOU!", after asking him if she can see Santa Claus with him, Marvin and Jeffy.
In "Jeffy's bad word", Mario accidentally calls a homeless guy a fag*ot (in a comedic way) in front of jeffy. Jeffy then repeats this word for the rest of the video 27 times until his dad spanks him to make him not say it and then Jeffy says it 2 more times after that.
In the episode: "Fat Jeffy", Jeffy says f*ck at least 20 times in the first 2 minutes with the video being 11 minutes.
Every single character in the series has sworn more than once.