system
A chat on subreddit /r/me_irl
human
Autism gets in the way of me getting the hint sometimes. I'd prefer it if people spelled it out, otherwise I'm going to assume they're either busy or forgot to text back (I do this alot, though it's usually due to depression). There are plenty of reasons someone may not text back for and as long as they're not spam texting (this post is an example of that) I see no harm in sending messages after not hearing back in a timely manner (following Googles advice of waiting a few days). I'd also prefer something besides a simple "hey" or "how are you doing" because it makes me feel like I'm supposed to carry the conversation that the other person started.
gpt
I get it. It's not perfect, but sometimes explicitly saying "stop talking to me" or "I don't want to talk to you ever" can cause people to flip out, cause a lot of other issues, etc. Some people don't take rejection very well.