Personnaly, I see nothing wrong to indicate that in.your TOS, especially if drawing character from those fandoms makes you uncomfortable. I also agree with Talikira and HEAVENDELUXE you don't have to tell your reasons, too ^^ Peoples do not buy a product, they buy a skilled service provided by a person with their own thoughts, feelings and boundaries ^^ 

i think you're good honestly. i don't do fanart commissions for this reason (among other things), otherwise if someone says they want you to draw a fan character from one of the things you don't like, you can always just say you're not comfortable with that

This seems like your version of not drawing gore drawings (or an equivalent). What I mean is that it’s ok to have restrictions on what/who you draw. Especially if you have an explanation for doing so, then whoever is commissioning you should be understanding of the circumstance & support you by honoring your request. 👌✨

Nothing wrong with that especially if it makes you uncomfortable! Unfortunately as artists we wind up getting bad memories associated with things, most of us should be understanding of one another’s boundaries. 

If you do t want to draw it for whatever reason then you should not have to. :) Talikira said it perfectly.

You're not a mega company, you're a single person with your own thoughts and feelings and you're allowed to add whatever rules and such you want to your commissions. If someone doesn't like it then they can just go elsewhere :P I've definitely seen people say they won't draw for certain fandoms or at all and I've never seen them get any flack for it. Do what you want/need to to make yourself most comfortable!

I totally agree with what Talikira said and I've seen many artists who won't do fandom characters and media characters in general and it's totally okay! People have their reasons and you don't need to say why as they are your boundaries 

I don't really mind much if they don't accept comms of characters in certain fandoms!

But if you want to do it, you could write it under your list of things you will not draw since I don't think you need to explain why so in your TOS imo because most people won't likely to pry about it.

If you already have a "will not draw" type of section in your ToS, you could probably just nest it under there like "will not draw from the following fandoms:" and just list it, you don't have to get into detail why! Another wording could be something like "will not accept characters or fan-characters from these IPs:"

It's not any of the consumer's business why you will/won't draw something, they can ask if they're curious and you can respond if you want. That's my 2 cents!