Here in Louisiana, or at least its rural areas, it seems that what brand of truck you buy is equivalent to say, supporting a team. You are expected to buy only one brand, ever, and ferociously defend your brand choice. This seems only apply to trucks, cars don’t seem to enter into it ever. Has anyone else noticed this? Or any other odd competitions?
I know a few guys who are insanely loyal to various brands of macrobrews. If their college frat only drank Miller Lite, they only drink Miller Lite. They actually get upset if only Bud Lite is available. Seems odd to me, but I suppose I can be slightly the same about Guinness.
My husband is like this but with Old Style. If a place doesn’t have Old Style, he won’t drink beer. This makes going to the track quite expensive, by the way. Me, if it’s beer, I drink it. As long as it’s regular beer like Bud. None of that fancy shmancy stuff like Heineken or Special Export or anything for me! 
OUr Dutch consumers magazine ran a feature on different brands of beer two yeras ago. They had a couple of self-identified “this is my brand and no other brand will do”-guys join in a blind beer-tasting test. The guys failed to recognize their own “favourite” brand ! When asked which brand tasted best, all chose different brands, and there was no correlation to the brand they said they preferred.
Sobering. 
About the OP: accents. People here see their accent, the way they speak, as a big part of their identity, and take great pride in having, keeping and passing on the accent they were raised in.
An accent I can see. That is part of your cultural heritage. A Chevy isn’t. Though I suppose something similar to that may be applied to it, as in “My family has bought this truck for years, and I’ll be damned if I change it.” That makes a lot of sense, actually.
High-school football teams in small-town West Texas. I’ve seen few things sadder than someone devoting their entire life to fervently supporting the town’s team.
I haven’t seen it quite as much lately, but Ford/Chevy divide didn’t used to be limited to trucks.
I’ve only owned one Ford car in my life, and I wasn’t happy about it. I’m a GM guy that drives a Toyota (because Detroit sold out anyway)
Even today, if someone gave me a fancy new Mustang I’d immediately sell it, but Ford trucks are ok.
It’s not rational, and I freely admit it.
So far, all the examples given have been men who were irrationally loyal to something. How about women?
Small-town high-school football. The women go ape over it, too. It’s often the overriding force in every resident’s life, male and female alike. You have to see it to believe it.
My undergrad university, I suppose. Our school spirit verged on the cult-ish. I never got as swept up into it as some did but I will freely admit learning the school songs and cheers while I was there. It was pretty contagious.
Oh, and MAC Select Sheer Facial Powder.
People are loyal to Apple products in a manner that verges on religion.
I know what you mean. I’m a student at Virginia Tech and the rivalry my school shares with the University of Virginia is absolutely ridiculous. My class ring features a tiny image of foot ball fans holding a sign that reads “BEAT UVA”. I have a step-sister and several cousins who went/go to UVA and they all think it’s hilarious. Apparently UVA doesn’t take the rivalry quite so seriously.
Programmers. They can make a religion out of what programming language is best, what OS is best, heck even what editor is best.
College football.
Particularly when the people in question didn’t even GO TO THAT FREAKIN’ COLLEGE!
I say this because I attended UT Austin. And I only knew when “we” won a sporting event because the UT tower lights turned orange. Oh look! We won…something!
And yet I now live in San Antonio and I bartend and during UT games, people are decked out head-to-toe in burnt orange, and carrying flags, and screaming and yelling…and I’d say that one out of ten of these people even WENT TO UT.
If I ask, they’ll say that their father-in-law, or their husband, or their friend-of-a-freakin’-friend went there…or that they just “love UT cuz their dad did,” or they “just hate A&M” [rival school] regardless of rhyme or reason.
Seriously? It’s bizarre to me. Fanatic loyalty to your school has always baffled me, but it makes more sense than fanatic loyalty to a school you’ve never even seen in person!
Chefs and weekend-warrior cooks can be intensely loyal not only to a maker, but of a specific kind of knife.
Me? I’m partial to the Wusthof knives. The Classic line. Henkel’s or any other maker are just … well, meh.
And though I own 13 different Wusthof knives, I usually reach for the 10" or 8" Chefs knife.
Language/OS wars will go on, but I thought the editor thing was long settled. It’s Emacs.
D&R
Ditto on the jaw-dropping regarding fanatic devotion to college teams from non-alumni/ae, and the “high school football” thing in small town Texas. I mean, these are high school kids playing…
Substitute “UK basketball” here and you characterize the average Kentuckian, most of whom never went to college, period.
When I was in high school in Texas, one of my dad’s friends (a good old boy and a Chevy man) gave me endless shit when I bought a vintage Ford Mustang. The usual “Fix Or Repair Daily”, “Found On Road Dead”, etc. It’s definitely a culture.
It’s a little hard to get excited about a rivalry that’s so one-sided. At least when I was there, we thought of Maryland as our main rival. I didn’t consider that much of a rivalry myself, but that might have something to do with growing up in Columbus…
The Cleveland Browns.