Is it disrespectful to refuse a henna artist?

No, it’s not disrespectful to refuse a henna artist — a polite "no thank you" is completely acceptable, and in tourist squares it’s wise, because some henna artists apply it uninvited then demand payment. Firmly declining and keeping your hands to yourself is the sensible move, not a rudeness.

In Jemaa el-Fnaa in particular, be careful: don’t let anyone grab your hand to "show" you a design, as that can lead to a charge, and be aware that some use black "henna" (PPD dye) that can cause skin reactions. Keep walking if you’re not interested.

If you genuinely want henna, agree the design and price first and seek out a reputable artist, ideally through your riad, using natural reddish-brown henna. Otherwise, a clear refusal is perfectly polite and protects you from a common hassle.