People who think that it requires gadgetry to control a horse.
People who think that if you use a gadget at all in training then you're "abusing" the horse.
People who don't understand that there is a purpose for a curb bit, and that when used correctly they can be great tools.
People who think that every horse must wear shoes/eat grain.
People who think that no horse needs shoes/requires grain.
People who look at someone trying to work with a rank horse and laugh and say how much fun the horse is having or how pretty he is when he rears/bucks/kicks out.
People with major and unaddressed horsey behavioral problems telling me (as I sit sideways in the saddle, my horse standing happily on a loose rein)that I'm doing something wrong in my training.
Show judges who judge every horse in an open division as a foundation QH (or tb, or pony, or...)
And... to finish...
People who think that The Black Stallion is real, and that their first horse can be a rank Arab stallion and that within a week they will be galloping tackless down the beach.
Wow, all of these peeves start with people... I must be antisocial, too!