Why guys do that thing they do when they hold a girl's hand?

like when they stroke your hand with your thumb?

its habit, simple as that

in all the movies and everything, it shows stroking their hand, and growing up you see it everywhere when people hold hands, so its what they know. Its a natural reaction to holding a girls hand. I have not met a single guy who DOESNT do it.

Its habit

I asked my boyfriend why he does it because I'd never really thought about it and he said he does it to keep reminding himself that he's holding the most precious person in his life =D this most likely doesn't help but ya know =L I think its just a habbit to be honest =L every guy I've met does it even if he don't know he's doing it =L