I've read that's to be expected, that you shouldn't expect to just have to say it once because they'll keep testing you a bit. Like if you tell that coworker you can't give him a ride home, he'll likely keep asking, maybe accompanied by some sort of guilt trip.
But I get so angry. Should I express that anger, or should you just be calm and robotic?
I'm one who internalizes a lot, and people are often surprised when I finally blow my top, so I'm wondering if displaying irritation would make them less inclined to continue bothering me, but I struggle with cognitive empathy, so it's hard for me to predict stuff like that.