Look, how do you say "stop glaring at me pointedly when I'm sitting with your friends and walk by to the back of the room really, really slowly" or "stop going up to the cash register and asking if your order's ready yet if I happen to walk into the same cafe?" It's ignoring with a mean edge attached to it. Just plain ignoring is cool, I don't care. This feels really weird.
I can't talk to him because the one time I did say hi, he flinched and looked... revolted. I'm not talking to that dude. It's not worth it.
He's doing this because I broke up with him and had irrevocable evidence that he'd done me wrong and kept doing me wrong despite my continued requests that he treat me differently. Honestly, I try not to go "hey, that guy is just plain fucked up" the way I used to, but I'm having a hard time understanding why he's using exactly the same techniques as he does on people who are literally proven sexual predators.
.... I believe you may be too innocently generous to let yourself see what's really going on here:
He's just a jackass and this is an understatement.
You are what is today considered intelligent but it has bred into you an exploitable weakness that can be used by the perceptive jackass. You ask "why," in pretty much everything and your days in whatever varied form are spent trying to understand and answer "why."
Things concerning humanity often have no why; they simply are, or just happen.
Why did that man steal my car instead of all the other cars?
Why did that police officer pull me over for speeding instead of everybody else?
In your case, "Why is my ex being such a total jackass to me when that's so needless?"
He just is. There is no why, but you will keep looking for it despite it not being there.
"Why" in this case is a question you will probably never be able to answer and the more you think about it the more it will drive you mad. Thinking about the question will make you think about him and how he hurt you and is still hurting you.
Look, how do you say "stop glaring at me pointedly when I'm sitting with your friends and walk by to the back of the room really, really slowly" or "stop going up to the cash register and asking if your order's ready yet if I happen to walk into the same cafe?" It's ignoring with a mean edge attached to it. Just plain ignoring is cool, I don't care. This feels really weird.
Place your little finger against that one critical spot in anything and it will fall to pieces.
He's doing it for your attention; he wants you to feel weird. Write him off as dead, because he is not worth your time. May his glares pass right through you without harm or ascribing meaning to them. Notice them, as you notice anything else in the background but give him no value. To hell with what he wants and especially to hell with what he wants you to feel. Carry mace in your purse in case he tries anything, but otherwise the thought of him isn't worthy to enter your mind.
Wish him away without a thought or a sound.
Simply, he is a troll. Do not feed.