"Smacking" will earn you a smack

What's the one thing about people that drives you absolutely around the bend, dear reader?
I don't care how much of a "people person" you may be. Surely there's something—some habit, some nuance, some aspect—of other people that causes you to grit your teeth and dig your nails straight through wood.
For me, it's people who smack and chomp when eating. Believe me, if there is any one thing that would give me cause to quite happily shoot you in the area where the sun don't shine, eating your food loudly would be it. This is the sort of annoying stuff—among countless others—that children do, but by the time you've reached adulthood, you should know how to eat properly.
I don't know anyone who doesn't get annoyed when someone noisily chews gum. So why do some people tolerate or even think it's normal to make similar levels of annoying noise while eating?
Now we all occasionally make chomping noises when eating. The infrequent second of "smack" is to be expected. And, dealing with cankers or sore teeth or other mouth problems may give cause to noisy eating.
But, under normal circumstances, there is no—let me repeat: NO—reason whatsoever to smack and chomp while eating. Don't give me this "well, you have to masticate your food thoroughly" business. And please don't also give this "I enjoy my food" shit, because I'll take your beloved food and throw it out the window. 
Take a morsel of food, chew with your mouth perfectly closed for as long as it takes, swallow it, repeat. That is the way to eat. No excuses.
As for people who eat noisily, with their mouths open, they are either completely without manners, were brought up by wolves or other animals, inbreds or completely retarded.