Once I read somewhere (now it's a cliché) that the worst is not dislike, but it's indifference. Because a person who dislikes you still cares. If they make you upset, you can still annoy them. But you can't touch a person who does not care, who is not aware. They are out of the reach of your influence. Their unresponsiveness is not because they want to seem detached (if this was the case, it would be a sign of caring) but that you are not a matter of importance to them. They overlook you.
They don't do it on purpose, so you can't really accuse them of being a bad person (if that would change anything!) They just don't care about you, and that's not a crime. Your hands are tied in front of them.
The best thing you can do is to remain indifferent for as long as possible. Unfortunately, the moment you try to stay indifferent, you have already entered the territory of conscious action, from which there is no return. Every time you claim you forgot someone, you confirm that you haven't. If you have really forgotten, you would not be thinking about them at all.
You understand the value of indifference once you lose it. It's like health. Cherish every moment of it.
My only consolation is that there are so many people I'm indifferent about, I wouldn't even be able to point them out to you (if that helps!)