I contemplated several characters, but in the end I choose this one: Chibi-Usa a.k.a. Sailor Chibi-Moon
I hate this character. She's bratty, spoiled and annoying as Chibi-Usa and next to useless as Chibi-Moon. She has a crush on her own father, that's not cute or charming, that's creepy. Nobody is ever really mad at her, no matter what kind of stunts she pulls, everybody has to love her if they're a good guy and to top it of, she's at fault for almost getting everybody in the future killed. And just because she couldn't keep her grubby hands of the silver crystal.
It pains me that my second favorite senshi, Saturn, ends up being so close to her. Chibi-Usa is neither lovable nor funny and then I had to suffer through an entire season with her at the center of the plot. Argh! Sailor Stars seemed like a heaven-sent because she finally left again and this time for good.
I admit, not my best post, but I.Just.Can't.Stand.Her! The only time I like her was as Black Lady and even only then because the transformation and her new look was cool.
Something Usagi's future self should have done more, maybe Chibi-Usa would have turned out better.