I agree with @tups
Bandying around the word narcissism has become a pop psychology fad the last handful of years, but…educating oneself about the nature of this condition is very enlightening. It sure explains a few people I have known in my life.
Another really HUGE red flag is the inability to accept ANY, criticism whatsoever without extreme reactivity and anger. Healthy people can handle confrontation and correction, or discussion about something they do that one finds offensive.
They are extremely fragile inspite of their blowhard and smug presentations, and even the slightest confrontation, correction, or complaint will turn them into raging, blame shifting infants.
Best “test” for ANY person you know is how they handle criticism and healthy confrontation. If they can’t handle even the gentlest of confrontations involving others feelings about something they have done, run!
You can’t argue with a toddler and the slightest insinuation that they have made a mistake is met with extreme defensiveness and anger. They NEVER apologize, NEVER, and will always find a way to make you the bad guy for daring to confront them.