I guess it's time to say my methods:
1. If you email me more than twice with a request to "Add me back, add me back," you will be banned.
2. If you flame me without actually expressing your motive, you will be banned.
3. If you blatantly, deliberately start a clearly avoidable flame war anywhere, anytime, on any web site, you will be banned.
4. If you are generally caustic, you may be pre-emptively banned, but asking nicely may get this lifted.
5. If you act in any of the above ways to any of my friends, you will be banned.
Really, I'm quite tolerant, no matter how this somewhat irriated post may sound like. But I have limits, I mark them quite clearly when they're being approached.
NOTE: Nobody on my friends list has even come close to any of this, so if you're on it, It's Not You(TM).