Inappropriate language

YouTube's monetisation guidelines list profanity as one of the categories that can restrict advertising, and moderate swearing is generally fine. Placement is what caught creators out. Strong language in the first 7 seconds once pushed a video into limited ads on its own, and after the complaints YouTube relaxed that and re-reviewed uploads demonetised for nothing else.

The leniency is specific to language. Graphic violence gets no equivalent allowance, and gore in gameplay footage can limit a video wherever it appears. Constant swearing across a whole video is still assessed differently from one word in the opening line.