My son doesn't hold his correctly. Drives me mad. He's right handed and holds his knife in his left hand. Because he's always done it he's crap and cutting with both hands.
I'm always surprised how many people hold their cutlery correctly generally, not just on TV shows. I can't work out why they were taught to use their knives and forks the way they do - apart from looking awkward, it's often really inefficient and I wonder what they do when they get a tougher bit of meat (or a blunt knife!!)
It's that, plus people who hold their writing instruments peculiarly - but the cutlery thing always strikes me as odd. They must have been brought up by people who didn't know the rules (or didn't use cutlery)
I used to work with someone who held both her knife and fork like a pen! I found it really distracting when we had a meal together as I would be completely mesmerised watching her trying to cut meat!
I am left handed and use my knife and fork in the correct hands and correct manner, I can however use my spoon in my right hand - no matter how much my mother used to slap me!!