deborah, do you have particularly loud exhaust? when you split, do you do so in a lower gear and higher revs? that could be a factor. might not be.
we could argue all day that it's your perception and not reality, but, to me, well, we're not there.
about the only thing i could add is that some dudes in cars would rather be on bikes but can't or won't, for whatever reason. sure, the old story is that the wife won't let them, but just as often, their driving behavior or mindset won't let them. regardless, some of these have-nots subsequently hate the haves. and, yes, they're assholes to male riders as well.
so, my theory is that it isn't the fact that you're female that earns their ire, it's your stature. all riders earn their ire, but if they know you're female, then the logical assumption is that, if it came to a physical confrontation, their risk is low. thus, they're willing to flip you shit they wouldn't to dudes.
let me throw some evidence behind my theory.
from behind, i am often mistaken for female. well, not so much now since i had all my hair chopped off last week. but, up until then, my ponytail was almost waist-length. that said, i'm 6'2" and weigh in at a svelte 250. so, people's first, gut reaction is that they're looking at a girl. very quickly, however, they realize that, even if i am a girl, they don't want to have anything to do with me. and of all the riders i have ever known or ridden with, i have always had the least on-road conflict and threat.
edit: and i should add i ride a very, very visible "LOOK AT ME" bike. i do so because they do see me, which is partly why i rarely find myself in dangerous situations. but what i mean is that the visibility of the colors you are wearing doesn't, in and of itself, to me, mean trouble.
but here's the funny part. everybody keeps telling you to speed up, and i don't doubt this, but i am the slowest rider i know (connie can attest to that

). make what you will of that.