If their saber isn't drawn and you have started started fighting, fair enough, since there is such a thing as courtesy (thought you wouldn't think so with some of the people out there :> ), but once combat has started if they turn off their saber it's either gonna be part of the feel of the fight, or because they caught the off key (like I do occasionally).
Once the fight has begun, if you turn off your saber, don't expect the other person to stop.
Simlarly, if they go into chat mode just as I'm about to hit with a killing blow, they had better expect to die. If they break off obviously, and then go into chat (and actually SAY something), then I stop and wait for them. And I give them no quarter if they prove treacherous.