Sara simons of Washington writes in with a tantalizing celebro-thetical etiquette problem: "When two celebs meet for the first time, do they introduce themselves, or is it just understood that they know each other's identities? I would introduce myself to Brad Pitt, but certainly not expect him to introduce himself in return." (Because, duh, he's Brad.) "If Tom Cruise and Eminem were to meet at a Lakers game," Simons continues, "do they just nod in acknowledgment of their mutual celebrity and jump into conversation? And if a lesser-known celeb meets Madonna, does she just introduce herself ('Hi, I'm Haylie Duff!') but not vice versa?"

From attending way too many red carpet events, observing from my quarantine behind the velvet ropes, I can tell you that proper celebrity manners dictate that both stars should present themselves, faux-humbly, to each other, as if sharing equal wattage ("Hi, I'm Brad"; "Oh, hey, dude, I'm Nick Lachey"), and of course, say something effusive about each other's work. These rules apply only in a room full of other human beings -- and in celebrities' lives, most rooms are full.

It would be embarrassing if one celebrity had never heard of the other, but fear not: Just as you or I might be vaguely aware of the key employees in other departments at the office, celebrities almost always know who's who. The interdependent Hollywood systems of management and publicity virtually ensure that celebrities (i.e., "clients") are aware of one another's existence and status.

Of course, gaffes happen. Two stars can end up in the same greenroom and not know (or pretend to not know) who the other is. This is another great reason celebrities don't leave the house without a phalanx of personal assistants, all of whom function as human Google machines, room-workers and headset-wearing ambassadors of goodwill, leaning over to discreetly whisper to their boss, just in time: That's Ashanti. You met her last year at that P. Diddy fashion show. "Ashanti! How are you? I just loved your. . ." -- album, "Concrete Rose" -- "albummm, 'Concrete Rose'!" etc. Very few celebrities just "bump into" one another -- at a club or while taking their courtside seats -- without getting a split-second heads-up from an aide. The ultimate Hollywood rule stands firm: Have your people call my people.