How are people so easily upset?

[Breadstick]

I'm selling a C10 I had previously and put the ad on Facebook marketplace. It has a clean title, runs and drives, and has lots of extra parts. I listed it for a VERY reasonable price and thus person came back with a no word offer, just the number which is half of the list price. As you can see by my reply, I think I was more courteous than her blunt offer deserved. She immediately got seemingly upset for no reason. It wasn't worth a response because the argument isn't beneficial, but how do you get so obnoxious out of the blue at a stranger because you don't get your way?