You know this guy
Hell, you may have been
These people for whatever reason, seem to think they are the only person there. That grumpy guy in the line at the post office who cuts in front of everyone because his business is simply *that* important? That woman who pushed past you in the grocery store isle because she was so intent on those prunes? The guy who pulled your clothes out of the dryer so that he could use it *now*, and without paying to boot?
For whatever reason, there seems to be a preponderance of people in our society who think that all those other great apes walking around in GAP and Khaki are not real people. Therefore, they can act in any way they wish, and no one will complain. And for the most part, they are correct. I've very rarely seen someone point out the reprehensible behavior of the only person in the room to them. And when it is pointed out, the only person is often shocked and angry at the percieved offense.
The only people who irritate me more than this are "the only OTHER person in the room". These people only recognize that there is a single other person in their vicinity. Ever been on a date, and your other half treats the waitress like some sort of food-fetchin' robot? Ever been in a class where there was that one guy or gal who talks directly to the teacher, interrupts their classmates with a comment or question - to the teacher, and generally acts as if your prof or teacher is there simply for that persons benefit?
These people irritate me more simply because, in many cases, the person that the only other person recognizes does not point out this rudeness to the only other person. Having done food service, and having several friends who have done food service, it never fails to amaze me when someone treats a waiter like a slave around me.
This usually results in some smacking around by a clue-by-four.