He Had Dangerous Delusions. ChatGPT Admitted It Made Them Worse (wsj.com)

To be fair to ChatGPT, in this case it seems unlikely it actually caused the manic episode; more likely, it simply made it worse. Not that that's much better.

On another note... has anybody figured out some custom instructions to prevent ChatGPT from being so flattering and obnoxious?

The sycophancy is obviously intentional. People are vulnerable to it, and addiction is profitable. It has nothing to do with the nature of LLMs and everything to do with user engagement metrics.