I think there's a huge difference between constructive criticism, and flat out criticism.
For example, what can someone possibly gain from being told their teeth are crooked? I realize that was just an example given... But still, what good is it going to do them? I'm sure they're well aware.
I used to get made fun of non-stop when I was younger, because I was so bad at sports. I knew it. I didn't need anyone to remind me... But because they did, it sure as heck kept me from playing sports (even for fun) for a long, long time. And actually, to this day, it takes a heck of a lot of coercing, and the promise of an ice cream cone, to even get me thinking about playing sports for fun.
"And death is at your doorstep
And it will steal your innocence
But it will not steal your substance
But you are not alone in this"
“My ability to turn good news into anxiety is rivaled only by my ability to turn anxiety into chin acne.” - Tina Fey