Don't show up late to your own ride ( I've done this but it's still stupid)
Don't show up to somebody else's ride, then try to form your own offshoot. That is stupid and lame. You shouldn't have shown up in the first place if you weren't going to participate.
If you aren't ready to leave when the ride is supposed to start, you are making everyone wait and that's rude. Just because you showed up at 8:59 for a 9am ride, we aren't going to wait while you pump up your tires, put your bibs on, and grab a coffee.