It amuses me how many variations we have on this:
"But, NE means watching out for yourself first and foremost..."
BZZZZZTTTT.
No. I'm going to directly contridict the player's handbook here. Read the description of NE and CE and see if you can see a real distinction. I can't.
CN means watching out for yourself first and foremost. That's clear from the definition of a pure indivualist. You, and the PH, clearly have NE confused with CE.
Neutral Evil is very VERY VERY hard to play correctly or even understand.
If your motivation for your evil acts is self-interest: revenge, amusement, greed, whatever - then you are CE. CE is the idea of furthering yourself at the expense of everyone elses, indeed the only way a CE percieves you can ultimately advance your own cause is on the backs of other people. Competition and scarcity of resources is what its about, and might makes right.
If your motivation for you evil acts is 'the good of the cause': your nation, your family, your belief system, then you are LE. This is the alignment of the acquesition of power to preserve and expand - your way of life, your race, your species - no matter what the cost. LE's see power as the measure of the worth of a society. Laws exist to increase and expand power. Subjects exist to serve the law. Rulers exist to enforce the law and expand the laws sway. Mercy is weakness.
So what is NE? The opposite of NG. Neutral good is 'Good for its own sake.' Good as an ideal, not a means to an end. So, NE is
EVIL FOR ITS OWN SAKE.
Destruction for the sake of the pain it causes. Really nuetral evils, that is to say pure evils, don't like doing what they are doing. If they did, they'd at least be obeying a drive - self gratification - to obtain a good result (pleasure). Nuetral evils are motivated by a hatred of life and even existance. They are nihilists without the joy of anarchy and rebelion or the pleasure found in the company of a subculture. They are universally destructive: destructive of themselves, of the society around them, and any individuals they come in contact with. They do evil SIMPLY because they BELIEVE in it, not because they expect to enjoy it, profit from it, or expect the world to be a better place.
Negating the description of Nuetral Good (which is far too short anyway), we get:
"A NE character does the worst that an evil person can do. He is devoted to hurting others. He works against kings and magistrates, but does not feel particular antipathy to them. Vile, a cleric who hurts others according to thier weaknesses , is neutral evil."
No human, with the possible exception of a sociopath, can truly grasp the enormity of nuetral evil. And even they kill to obtain some sort of temporary release. Most human NE's probably couldn't explain what they do. They just do.
I've yet to meet the person that really enjoys playing his character as a NE. I've meet ALOT that like the purile escapism and ego tripping of CE, and let me tell you - that can get old really fast. I've no respect for DM's that encourage that sort of thing.
I've yet to meet a well played LE character, and think that would be interesting. LN comes in second among least used PC alignments.
I personally think I'd find Neutrality the hardest to play, and the most constraining on my actions (though power gamers tend to find it liberating). I care too much for apethetic, and I don't understand the appeal of 'balance' (So half the world sucks and is miserable, what's so great about that?). The only way I could play it would be as the friend of some more motivated person in the party, who was adventuring because in a sense, it was just going along with the flow.