I'm understanding when people don't know this about me and try to give me affectionate physical contact. If it's a one-time thing I'll let it slide, but if it starts happening a lot (some people are just much more likely to express themselves physically) I will explain to them, "Well, thank you, but actually I don't really like to be touched. It's not really my thing." Most of the time, they just go, "Oh! OK, I didn't know, I'll try not to do that again," and we're all fine.
And then... sometimes things like this happen.
I had an encounter once where I ran into a couple people who I know are particularly touchy-feely. I knew they were probably both going to try and hug me, and I simply didn't have the energy to deal with that. So as I approached them, I said, "I'm sorry, I'm not feeling well today" (not entirely true, but it's a good introvert fallback phrase). One of them said out loud, "No hugs today, huh?" and I sort of smiled back and said, "No, please, not today," and walked past them.
One of them then chased me down and hugged me anyway. When he finally let me go, he said he hoped I felt better and I left.
This made me angry me for at least a week and a half after it happened.
I have similar experiences every once in awhile. Usually it's extroverts who do this to me, but not always - sometimes just outgoing introverts (no, that term is not an oxymoron). I think they think it's cute or endearing or kind of a playful teasing action.
Well, it's not. It really, truly isn't.
It's one thing if you don't know. If I've never told you this, there's a little leniency there. And my very close friends who I feel comfortable with are allowed more physical contact (on good days when I'm not tense or on edge).
But if I outright say I don't want to be hugged in that moment, and you ignore that and hug me anyway... that's harassment. Even if you didn't mean it like that, that's what it is. You've decided that I don't really mean it, that it's not really that big a deal, that you don't have to follow the rules I've presented. Except, uh, you kind of do. Because this is my body and if I say you can't touch it, then you can't touch it. No matter how innocent or playful it's supposed to be, no matter if you think it'll cheer me up (you're wrong). If you step over that line for any reason, you make me feel uncomfortable and unsafe.
Personal boundaries aren't a joke. They really aren't. And ignoring them makes you creepy.