I cannot stand 99.9% of anime, but I have very specific reasons. For me, the most prevalent is that EVERY SINGLE anime out there just HAS to have the absolute most annoying high-pitched and shrill female voices for the female characters... I cannot stand the female voices in anime... they sound so gratingly childish and shrill... and loudly so.
The second reason is that again, no matter how "serious" the mood or story of a given anime, EVERY SINGLE frakking one has to have some super-childish and uber-"cutesy" little creature or robot with nothing but a pair of eyes that's meant to convey a feeling of such sweetness and uber-cuteness that one look can induce a diabetic coma. Such creatures or robots usually only communicate in equally demure and "cute" beeps, whines, or squeaks. Hell, I saw one anime where the freaking A.I. of a damn starship was one of these cuddly-wuddly fuzzballs with eyes... are you frakking kidding me?
So yeah, those are the main reasons I do not like anime and cannot stand it. Those two elements most of all not only irritate me to no end, but prevent me from being able to enjoy the actual story, and take me out of the mood... especially the cutesy creature stuff... ugh.