I almost always send a Tell following some kind of IC conflict, being that I often clash with other characters because of alignment and beliefs. There's absolutely no sense in having bad blood OOC because a situation isn't handled with reasonable courtesy from one player to another.
That being said, I think this is all especially pertinent to some of the IG goings-on right now. My $.02 is that you should definitely grab a DM if you're going to have conflict of this nature, if for no other reason than to ensure at least a better chance at fairness (or at least moderation of some sort).
I also agree with the point that if you're going to be intimidating another character, it goes a long way (for me personally as a player) to see that you have a +8 Intimidate modifier, rather than you just expecting me to play along. I know not everyone's a fan of social skills, and they definitely don't guarantee an automatic response of any kind from other players (nor should they), but they at least show that you've put thought into the persuasive/beguiling/intimidating/taunting nature of your PC further than demanding someone fear you in front of NPC guards.