In my area most of the hate is directed against Eldar, at least most of the vocal hate. Personally, the army I dislike the most is necrons. I had quite a chuckle when a necron player was saying something about how sure Eldar have weaknesses, but they have ways to compensate for all those weaknesses, so they really don't have weaknesses. I thought, hmmm, that sounds familiar. I know an army that has a better statline across the board (except inititive), that has the most useful basic weapons in the game (so much so that there is no need for any dedicated antitank weaponry), can have as many as three save opportunities (SV, WBB, Monolith WBB), is not too good at CC (though it still has a WS4???), but can pull two or three units out of cc with little difficulty leaving the CC unit standing in the open to get shot to pieces, has no pressing need for cover since it can be guaranteed saves even against the nastiest of weapons... The res orb nullifies any attempt to deny WBB. Veil and the Monolith save units from cc. There are great counters two the two biggest weaknesses that necrons have. And he was complaining that Eldar can compensate for their weaknesses.
Perhaps the most anoying thing about some necron armies is when they just gather in a tight cluster and stand there shooting you the whole game. There is little in the way of tactics involved in ensuring the whole army is in veil and res orb range, then just rolling dice. It is annoying when an army can be very successful with such a simple plan. And when there are 10-15 destroyers supporting the large warrior squads, you can pretty much forget about denying wwb rolls by destroying the whole unit. You have to have some serious firepower to drop 10 destroyers in one round of shooting (don't know if I ever dropped 10, but I did drop 9 of 9 once, wraithcannons, mmmm), and if just one of them happens to be hiding out of line of sight, it won't matter that you drop the 9 that can be seen because they will just get right back up again.
Ok that was a bit of a rant about what is annoying about necrons. They are the hardest army for me to deal with personally, particularly with my DE (they have great counters for everything), but I enjoy challenges. I try to limit my vocalizations of the annoyances of necrons (online to a bunch of people I don't know doesn't really count) and focus instead of developing ways to beat them. The challenge of cracking that code is enjoyable, as is using a cheap throw away squad to lock necrons in HTH so that they will be veiled out and nicely packed for three destructor blasts (wound on 2s, ap3) from my ravager, or nicely packed for horrorfex shots (pin test at minus how ever many models are under the blast, 10-7 = 3, have fun passing that one
).
Necrons have to be approached in a manner very different than any other army. This proves very frustrating to anyone who isn't willing to spend the effort develping a different set of tactics and mindset. In some ways that is the same thing that causes many to dislike Eldar so much.
If your gaming group can't handle the challenge, and if you manage to win almost all the time, why not create a tougher challenge for yourself by using less than optimal builds. If they have a bit more success, they may have their perspective slowly changed. You will also get better by learning how to win with different less effective tools.