BAD IDEA
Is it a red flag to reply to messages quickly?
No, replying fast isn’t inherently suspicious, but if you’re a robot, it might freak people out.
Responding quickly to messages is usually a sign of enthusiasm or good manners, not a warning sign. Unless you’re answering so fast it looks like you’ve got no life or you’re stalking someone, it's just being respectful. So, no, quick replies are not a red flag unless you turn creepy about it.