RP-I beg to differ (only becuase I love you so!).
I think it would be a red flag for you IF the person wasn't doing anything about it and wasn't interested, because it would mean that they weren't interested in caring for themselves-which is just as dangerous as someone who mistreats their pets, children, metamours, spouses etc.
That said-I do agree with the thoughts that RED flag might be overstating it.
It's something that I would only concern myself with if they weren't concerned about their own self-care. Because if a person isn't interested in caring for themself-they can't possibly care for me. Which isn't to say that they are responsible for me-but I like mutual care-taking in a relationship.