Didn’t the OP say “strange?” Most of these seem fairly common to me.
-People who wear t-shirts with bible verses on them. It strikes me as being insecure.
-White people (in my experience it’s mostly been men) who have Chinese or Japanese characters as tattoos. I always want to ask them if they really (no, really) know what it means. And it’s always Chinese or Japanese characters. What the heck is wrong with Korean? Or, I dunno, Thai?
-People who replace sugar with Splenda, or butter with I Can’t Believe It’s Not Butter, or any other “healthy” substitute when cooking. Yeah, yeah, I realize that diabetes and other health issues can complicate things, but whenever I see that I can’t help but think “use real food or don’t cook at all!”
-People who don’t like cats. Preferring dogs over cats is one thing, but disliking cats altogether makes me instantly suspicious.
A (white) friend of mine spent his teenage years in Japan. I met him in Hawaii in his early 20s; his last name is Godo and while in Hawaii he had the kanji matching the sounds “Go-do” tatooed on his calf. I don’t know what the characters he got actually mean (he did), but evidently they’re rather odd – when he went surfing, he used to get a kick out of watching people stare in confusion at the tat, mouthing the sounds and trying to figure it out.
No real relevance whatsoever, but you brought it to mind and the idea still amuses me. 
What gets me is when you ask someone if they like cats and they say “Oh, I don’t like cats, I like dogs”. It’s not a competition! It’s perfectly normal to have a preference, but just because you like one doesn’t mean you have to hate the other!
I “own” cats. People that like cats make me suspicious. 
People who think they own cats makes me suspicious
I have an irrrational hatred of people who put “treehugger” bumper stickers on their SUV’s. I don’t make hand gestures or anything.
I assume that people who have outside only cats or chain their dogs to a tree will treat their children the same way.
I’m prejudiced against men that wear shoes with hard leather soles that make noise when walking on hard surfaces. Bonus points if they are super shiny loafers. Come on, man…they have sole materials now that don’t sound like you forgot to change your shoes after tap class.
People with Corvette’s, Ferrari’s, Cobra’s, etc. that wear the jacket, t-shirt, sunglasses, and all of that. It’s a cool car, I agree, but you look like a jackass wearing all that.
Guilty! I have the Chinese characters for “knowledge” and “teaching” on my right bicep (as a souvenir from my first ChiDope). I’ve had two different people confirm that the right symbols were placed. To me, you can teach someone something new every day, and you can learn something new every day. It’s my own little fight against ignorance.
Of course, at a different ChiDope, I grabbed Ed Zotti’s crotch on a dare, so take the above for what it’s worth.
Glad you put that profession disclaimer in there. I’m a career cook, and let me tell you how irritating it is to constantly have crap under your fingernails. You get something under there, scrape it out, and two minutes later there’s something else under your fingernails. So I keep mine as short as I can trim them without hurting myself.
My strange prejudice: I think poorly of people who rage against rock artists who are virtuoso musicians. Usually they’re ranting about progressive rock bands whose members play with great skill, precision, and complexity, and who write songs that aren’t about partying, sex, and violence. They generally seem to hold the position that only “blues-based” rock is “real” rock. I want to shake these people and yell at them that “rock” as a genre is nearly 60 years old and that by now it shouldn’t all have to be angry and rebellious.
Also, I think very poorly of people who, in one breath, loudly proclaim that ‘Weird Al’ Yankovic is a “ripoff artist”, and in the next breath wax philosophically about Led Zeppelin’s groundbreaking originality.
I don’t prejudge people who do this, but it does cause an eyebrow raise, especially when someone unwittingly makes themselves look bad.
For example, one of the workers at my local DMV has his name, Mike, in Japanese characters on his forearm. Forget, for the moment, how somewhat silly it is for Mike to have his own name tattooed on his own body. What made it funny is he had it done in hiragana instead of katakana, so he had まいく, which could mean something like “go between”, instead of マイク, which is the correct way to spell out the English name Mike in Japanese. Sounding out the characters the first time I saw them, I knew right away what Mike’s intent was, but a Japanese person wouldn’t know what to make of the characters まいく tattooed on someone’s arm.
This brings me to the question I ask myself whenever I see Americans with Japanese characters tattooed on their bodies. If you can’t read the language, or even know the characters, how can you ever know that the tattoo says what the tattoo artist says it does? Hiragana and katakana are difficult enough, kanji, which is the syllabary used in most Asian-inspired tattoos, on the other hand, is much more complex. Two (or more) kanji that have distinct definitions individually can have a completely different definition when placed together, depending on context. In the wrong context, or with no context at all, the combination can sometimes make no sense.
I wore a linen dress printed with Chinese symbols on it to the mall one day and sat down on a bench. A nice elderly Chinese man sat down across from me and told me the symbols meant ‘luck, wealth, and happiness’. “Oh”, sez I, “they don’t say ‘I’m a chubby white girl trying to look exotic’? 
Well, all right then!”
I always think less of people who use apostrophes when pluralizing.
My rule of Thailand:
If you are a) a tourist, b) male, and crucially c) wearing a pork pie hat, you are almost certainly a complete wanker.
I thought of two more that were spawned by other posts.
I’m irrationally prejudiced against people that say “pop” instead of “soda” - to me that makes them practically a redneck.
I also believe that you’re not entirely computer literate if you choose to use Internet Explorer as your primary browser. Same if you are still using an AOL email address.
I grew up hearing it called “pop” by everybody I knew, in the Pacific Northwest (more specifically, western Washington state). I didn’t switch to calling it “soda” until I was in my 30s. I’d moved to eastern Washington when I was 17, to an agricultural town. At that time (1983) the Hispanic migrant workers were, indeed “migrant”, but over time many started settling here full-time, and now this town is about 30% Hispanic year-round. I decided that using “soda”, a word understandable to both English and Spanish speakers, made sense (especially since I’m in the restaurant business). But the decision to change was a language thing, not an “adult” thing.
It’s not an urban/rural split, nor does it have anything to do with family income or upbringing. It’s geographical. This is an enlightening map.
I’m irrationally prejudiced against people trying to reason other people out of their irrational prejudices.
Why should you have that prejudice? It’s irrational and useless.
[quote=“Gary “Wombat” Robson, post:377, topic:571296”]
It’s not an urban/rural split, nor does it have anything to do with family income or upbringing. It’s geographical. This is an enlightening map.
[/QUOTE]
I am aware of that. Doesn’t matter. That’s what makes it irrational.
In other words what fachverwirrt said. 