I'm American, I was born in TX & I lived all over when I was younger because my father joined the U.S. Military but he's a British National & so is my mother, or they were, they became citizens about 30 yrs ago now. Since my dad retired & moved us to NH I've lived in & around New England for the past 20 years. My accent is probably someplace between Stephen King & Steve Earle! But I remember my mum & dad using the word when I was a kid, & I was always under the assumption that it meant a positive attitude or being excited about something, not angry or pi**ed???
Not that this has anything to do with the O.P. but I think just about everyone has written that guy off by now anyway, so why not???