We can do without the chest thumping
Many feel that the .22 isn't a "macho" round, and shun it for that reason. It's for training and small game, not personal defense. And, as far as that goes, they are right. About the training and small game, that is.
Bullets entering the body and striking bone do one of two things. The smash through the bone (often changing direction while doing so), or the "bounce" off the bone, changing direction.
The fellow you met is an under educated braggart.
A "standard" .22 RF is the lowest power cartridge commonly available. The .25ACP beats it by a very small amount, but falls below the hottest .22RFs. Every larger cartridge increases your odds of stopping an attacker. And its all about odds. We use HP or SP ammo over FMJ to increase the odds. We practice to increase the odds.
The "lowly" .22 is not to be dismissed out of hand, many have died or been permanently injured as a result of being shot with it. Many have not.
As mentioned, a .22 killed Robert Kennedy. A .22 put James Brady in a wheelchair for life. A .22 from the same gun shot Regan in the chest, and only inflicted a minor wound, from which he rapidly and fully recovered. A .22 in the hands of an attacker is no laughing matter.
The consensus of people who actually know what they are talking about is that a .22 for self defense is better than no gun, but inferior to just about everything else in terms of general effectiveness.
The number of deaths attributable to a given cartridge is meaningless. Germs have killed more people throughout history than guns, does that mean the best way to stop an attacker is to cough on them?
Since you already have a 9mm that you shoot, (and presumably trust your ability with it), no smaller caliber round could serve you any better, and it is highly unlikely to serve you as well. And thats not opinion, its physics.