One is if I hold a door for someone, and he or she walks through without saying thank you, that offends me.
I did that to somebody once. I was really distracted by some crap I was stressing over and I walked through the door, really not paying attention.
She said THANK YOU!
I, still off in my own world, said oh, uh, ok, you’re welcome.
I didn’t mean to be rude.
What offends me?
That an aunt (my father’s sister) and an uncle (my father’s brother) want me to give my grandmother’s ring to my uncle to give to one of his daughter’s so they can keep it in the family.
I guess I’m not family.
Counterpoint: when i have people race me to the door, ignoring my "no thank you"s just to get to it before me so they can be the good Samaritan, i never say thanks. Never. I just go thru.
Jeez man, they’re just trying to be nice. I kinda see your perspective: competency and independence. But they really just want to help.
I get offended when I’m 3 steps behind someone and they don’t hold the door. Assholes. 
People who spit offend me. I formed a really good friendship with a university student at my workplace, despite our age difference, and then he just started gobbing on the ground every 5 minutes or so everywhere we went. WTF?
Willful stupidity.
As in antivaxxers, general woo believers, and things like that, but also religious fanatics and any other kind of fanatic.
Stuck behind a left-turning car that won’t turn on the yellow and instead waits for the next advance green.
Honestly, it depends on the day.
Being offended at everything is exhausting. Sometimes a particularly egregious incidence of bigotry will get me really worked up. Racism. Misogyny. Homophobia. Misandry.
These days I feel like it takes a lot more than it used to.
Bad tipping.
If your server was absolutely terrible and cursed your family and got your orders all wrong and wouldn’t admit it etc etc - I absolutely understand.
But if your service was anything from normal to good and you leave less than 10%, that is offensive.
Shopping carts abandoned in the parking lot. It’s not onerous to return the cart to the corral, or even back to the sidewalk. Even if you have a small child in tow. The only time I don’t judge people for abandoned trolleys is when the cart is left next to a handicap parking space (on the assumption that someone was physically unable to return the cart.)
You must have epic good manners…
People discussing astrological signs in any way
IME those tend to be the people whose “help” involves getting in your way, which is not very helpful. I’m as offended by their incompetence as by the notion that I can’t open a door.
You must be a Scorpio.
::grins, ducks and runs::
If I let you into traffic, and you don’t wave or make eye contact, or acknowledge in some fashion that I just did you a favor, you get called a bad name.
Youve gotta be fucking kidding me. Did you read what i wrote? These people ignore my polite declines and continue on like i was only joking. Its easier, much easier, for me to get the door myself than have to wait and wheel underneath someone’s akwardly extended arm pit.
There is a reason i say “no thanks” and i would appreciate being respected enough to be listened to.
So they’re ignoring your “polite declines,” and you punish them with rudeness? Did it ever occur to you that some people hold doors open for everyone? Do you expect them to slam it in your face? I’ve been partially disabled for the past year, and I appreciate all the help I get.
The intelligence-insulting programming on television known colloquially as “news” offends me.
I hereby name it “Mr. Fuzzybutt.” Thank you for giving me permission to do so.
Dammit, took mine. That offends me that you are in my head. 
“Animal-rights activists” who only care about cute animals, or screech at the sight of a spider and try to kill the spiders. (Spiders are animals.) Hypocrite anyone?
This includes the “Save the dolphins caught in tuna nets, but never mind the tuna” folks.
Then there are people who pull out in front of me, cut me off, or otherwise violate my clear right of way, sometimes even causing me to slam on my brakes, then wave and smile at me like I had stopped and let them through on purpose.
Also, people who run red lights, but especially the ones who do it on my green arrow, so that I miss my chance to turn.
That doesn’t bother me, but I get offended when I’m 15, 20, even 30 ft behind someone and they hold the door for me, so I feel obligated to break into a trot so they’re not stuck holding the door open for a long time.