What could be the cause of someone having a habit of bringing their jaw inwards so their upper teeth appear ?

Question

to be sticking out, over the jaw, making them look goofy and not very bright? I have a relative from Ireland who does this when he's thinking and I am wondering what's up with him.

Answer 1

It's probably a long ingrained habit that he is unaware of, and is just a normal facial action for him.