Is it a red flag if someone only ever has good things to say about themselves?

Sure sign of narcissism. None of us are perfect, and lack of at least self-deprecating humor raises questions about their level of empathy.

Those that believe in "positive" thinking often only think about themselves.

There is a name for that, that has already been mentioned.

Not necessarily. It could be that they are practicing positive thinking re. themselves. Watch for whether they are also speaking only positives about everything and everyone else. A BIG red flag is when they are always right and everyone else is always wrong.

That's a strong maybe. I know people who think rather highly of themselves, but some of them are good people, others aren't.

I try to not look for faults/red flags. If I did, I wouldn't like me much.

Maybe, but it's an even redder flag if someone only ever has bad things to say about others.

If "only saying good things" includes never apologizing, never admitting mistakes, rationalizing their behavior when they hurt people, etc., then I would say it is a red flag.

But it is also possible that a person does not see me as someone to share their self-doubts with, and saves that kind of conversation for more trusted confidants. There is nothing wrong with that.

Despite the current cultural calls of love yourself more than anybody else when you see it in action a red flag goes up ...it's an absolute bore to talk about one's self all the time.
If this is a coupled with putting other people down you're dealing with a narcissist.

Not really. Maybe they are just a positive person. You’d need to factor other things in, over time, to really know.

Nothing worse then a selfloather

Maybe more of a yellow flag. From personal experience 😆, some people are genuinely awkward and have no idea that this is wrong. Many awkward people are amazing individuals who just haven't properly been taught social norms and expectations.

It’s a balance, but sure, someone who has only positive things to say about themselves (or somehow whatever negative things are never their fault/responsibility), is either an egotist or intentionally deceptive

When people jump into the dating pool, they sometimes try to project false images of themselves. The only other time this happens is when they are in the middle of a job interview...😉

Not really no. Takes more signs to be a red flag than just being comfortable in yourself or happy in life. I'd say it's a bigger red flag if someone can't handle that others are a cheerful person.

I wish I could be more like that but if they do it to where it becomes annoying then it's just annoying and stupid

True.

Also How many people do you know who openly confesses to every bad thing about themselves ?

Yes.
No-one is all good and that just comes across as self centered egoism with no self awareness.

Obviously. Humans need sound, rational judgement. This requires truth

If someone says bad things about themselves it's an instant ick

....red flag...of possible mental illness and HUUUUGGEEE problems ahead.

Yes, and one I should have paid attention to.

yes, and on that note, i'm terrible...

Depends on many things

Definitely

As others have stated, it really depends. Context is everything. The other extreme, someone who only puts him or herself down, can be even more problematic.

Nah, that's boasting and it's silly, usually people who boast a lot lack in confidence and are trying to match what they think you are (projection)

At worst they're annoying and insecure

I would say so, if someone can admit they have faults that’s a red flag.