Personally, if I'm super manic and someone brings up that I need help I'd probably start screaming either "No I don't!" or "Obviously, now what are you gonna do about it?!" depending on the type of mania. If someone says a delusion isn't real, I might say "okay, whatever," but I'll keep on believing it, but just not bring it up to this person (or anyone else) again.

You can gently say you're concerned, but you have to be prepared to not engage in any sort of fighting (it takes two to tango after all).