It's happened to all of us.
Might be something JohnRob could add to his upgrade list. Deaden the "Post" button for a minute after first click.
I’ve been on forums where I respond to someone, and then see a post that I immediately want to send a short quip to, and I get a “must wait 10 seconds to post again”. If I immediately try to post again, it will say, “must wait 8 seconds...” Etc.