When you run into someone you used to know, who disliked you

I don't think they will hate you forever. There are people I walk past from high school (I'm 21) that I don't say hi too that I've known for many years and its because I feel like they wouldn't remember me, or they might feel weird.
However, I don't have any hard feelings against them. Alot of people are this way and often times avoid contact. I think sometimes people don't recognize each other as well. It's unlikely that they care too much anyways even if they still disliked you. But there are definitely people I say hi too, especially if they seemed pretty open to talk too from the start and it goes well.