I think it might be more that the word doesn't have any redeeming qualities for you so it just gets to you more? I mean like if you hated gay people (I don't know if we have enough imagination to pull this off) then "gay" as an insult would bother you a bunch still because you wouldn't see any redeeming value in it and it would be pretty much 100% negative.

Plus it's also the laziness of it I think as well, at least for me it is. I get more aggravated when people do like "o ya u fckin bastrd! your just a piece of crap biotch who dont kno shit!" than if it were all proper. I mean seriously? If you're going to insult me, at least do it properly morons.