when replying that way in any way, on text or actually just saying “cool”. my friends say cool a lot and I really don’t mind it and my partner says it too but some people have thought it was rude and I had a friend say “that’s what I say when I don’t give a damn”.
To be honest I think it’s the trailing full stop that does that. Over text I find that usually comes across like you’re trying to shut down the conversation (even when you’re not)