Its definetly an online thing... Most of the dick heads that talk shit on here wouldn't say two words to you in person.
As far as Metalheads in person. I go to this Bar called the Brass Mug in Tampa, it's a pretty well known Metal club. I've met Glen Benton their and a few members of Cannibal Corpse, also Morrisound Studio is right down the street were many metal bands record like Iced Earth, Demons and Wizards and many more... Anyways, it's a shit whole and can be pretty intimidating to someone who's not customed to going their but I'd say 90% of the people are very friendly. Sure you have your few dick heads every now and then but that's everywhere. So I'd say most "Metalheads" that come across kind of harsh are usually only during online situations like this or their just young imature kids trying to act tough.