My biggest red flag is when all they talk about is them. And no matter what you say, they one-up you. I call these people me-monsters. Or one-uppers.

Neediness.

I have an indicator as opposed to a specific thing and that is my instincts. My instincts are usually spot on, whether I choose to ignore them is another matter and quite often where I fuck things up

The "F" word, faith. If you have it, you don't deal with reality.

Personally, I've been subjected to therapy on 3 different occasions, twice by my mother and once by the government. In each case, the therapists themselves personally told me that I didn't need it. I'm sure there are instances where it might help, but it was literally a waste of time and money. I'm just glad that the money wasn't mine, but I'd still like that time back.

If they're married.

No sense of humor would be second.

It certainly means he does need therapy.

Bad hygiene

Well what a hard question. My first red flag would be an outer superficial one like smoking.

Grammar errors.

Well to be more specific, my red flag would be any characteristics indicative of BPD/NPD...namely, Love bombing, triangulation, gaslighting, lies and secrets, narcissistic rage, devaluing, fake epiphanies and genuine manipulation...
No, not a simple answer. But well worth the education.

When a woman gets right up in my face and yells at me saying

You're a stupid insensitive chauvinistic ugly no personality no talent smelly sewer rat disgusting pervert then I sometimes think that may be sort of a little red flagy. I mean who wants a weirdo woman like that? Sheesh!

Talking over someone else ?

Nose-picking.

Fanaticism/zealotry, whether it’s religion, philosophy, or politics. For me, that all boils down to a serious lack of compassion, which is essential to humanity.

bad table manners and social behaviour. Very indicative of a person's character.

(It be very cautious by an overtly flirty sexualized encounter with a younger gorgeous sexy woman that would be highly interested in me while ignoring all other men. I would think it would be some kind of set-up or something sinister since I recognized I'm not that attractive nor interesting...)

I've never been with a woman that wasn't borderline or NPD. Our culture is horribly abusive to women. It's terribly disheartening for the empathetic and honest men/women seeking to share a balanced relationship

The absolute deal breakers are smoking, substance abuse, lack of integrity, and use of SSRI anti-depressants.

I have learned from experiences (plural used advisedly) that SSRIs literally prevent the formation of true, committed relationships.

Actually I have to disagree with your assessment. If the person seeking therapy has a high IQ, and the therapist does not, therapy has a lower rate of success. If the helper cannot out-maneuver the dysfunctional thought patterns of the helped, it doesn't work. I've actually had this conversation with past therapists, who agreed entirely with my assessment that they were unable to be of any help.