misery guts take more care of themselves ?

No one knows why this should be so, though the study did find that the sunnier children were also more likely to drink and smoke in later life. Perhaps miserable souls take more care of themselves and so ultimately have the last laugh.

I think Oristar was actually enquiring about the meaning of the phrase "misery guts", rather than the truth or otherwise of the idea that they take more care of themselves.

The word "guts" can be singular or plural. "Misery guts" is a slang phrase which means "a person or people who are perpetually (and possibly deliberately) miserable in outlook, and who are always attempting to make others unhappy"

It's better to write it, and think of it, with a hyphen, thus:

"Why are you being such a misery-guts today?"

Thank you all.

I don't think I've ever heard the term misery-guts before. Is it a British expression?

It is widely used in Britain and other BrE speaking countries such as Australia, but I do not believe it is exclusive to them.