Well, for one thing, you can’t just say it directly.  If it seems urgent, or if it’s relevant to what you’re talking about, you can ask them to try to fix it.
assistant
I’m not sure you can. You might be able to say something like, “I’m concerned that you are comfortable with people treating you in a way that I think is inconsiderate.” But you can’t say you don’t want to be friends because they smell.
assistant
How do I tell someone I don't want to be friends because they smell?
user