You know how it is, early in the morning, the brain fogged with too little (or occasionally too much) sleep, the sunlight a painful reminder that a new day has begun.   There you are, minding your own business and hoping that eventually two or more neurons will make some kind of concerted effort to get together in a meaningful long-term relationship, when you find yourself suddenly face-to-face with another human being.

"Good morning," s/he says.

"Hello," you say, "how are you?"

Now right there, you've made a big mistake.  Let's face it, you've asked a question for which you don't want an answer.  What if this person tells you about a death in the family or incipient surgery?  Worse yet, what if this person has no life and proceeds to fill your wax-encrusted ear canals with a stream of meaningless drivel?

All you ever wanted to do was acknowledge this person's existence.   "Look," you should have said, "I'm tired and confused and I'm not real sure where I am right now, let alone who you are.  I would like you to know that I bear you no real ill will for existing and later on I'll probably want to talk, but right now I just want you to go away so I can resume staring at the pattern on this wall and waiting for some miracle of spontaneous coherence."

Allow me to suggest the civilized early-morning greeting:

"ACE, man."

ACE is an acronym for the phrase "Acknowledgement of Continued Existence."  That's all you want to do.  "Yeah, OK, you're there, I'm here, the world hasn't ended, now go away while I finish waking up."  Just say, "ACE."

ACE is suitable for a number of other social situations.  Being in a hurry for an appointment.  Politely brushing off that witless boor in the office.   Returning from the dentist with a mouth full of novacaine.  It's polite, it's efficient, it's more civilized than standing there with a glazed look on your face or faking a sudden attack of incontinence (not to mention alternatives that involve the use of deadly force).

If you're in the military, you should probably use the variant "ACE, Sir!"  In the presence of royalty, use the appropriate respectful title.  Depending on conditions there may be other modifications that seem appropriate, but don't strain for them early in the morning.  In a pinch, a croaked "ACE" and bloodshot eyes should do the trick.

It is helpful to accompany the greeting with a desultory wave of the hand, palm towards the other person, with a tired pushing-away motion as if you would ward off contact with them if only you had the strength.  This mimics the body language used by people with contagious and debilitating colds when they are faced with social situations, evoking an automatic avoidance reaction in the other person.

We suppose that Emily Post (or her spiritual successor) would have some problems with this.  We can think of many arguments she might make against this somewhat brutal, if efficient, social mechanism.  Our response to her must remain fairly succint:  don't try to engage us in debate on the matter early in the morning.

ACE, man.