I don't hate characters, they can be annoying, but with history like theirs -long and rich- they can come of as *****ey (applies to good characters) or annoying at certain points.
Joker & Harley.
They are funny as a duo, Batman kicking the socks out of them is funny.
But yeah, leaving them alive after all the murders they did, especially after all the damage Joker does to Gotham and Batman's loved ones is just stupid from Batman's end.
I understand how in comics they need to leave a character live on, cause.. comics, but I wish Joker really dies in other media, like his death in Batman Beyond: Return of the Joker, or in the first Burton Batman film.
Red Tornado (John Smith)
I don't hate him as a whole, but much like Vision, I hate the concept of a robot having a soul, and hate it more when the robot feels love for a human, and the human loves back.
Wonder Woman
I like this character, I really do, she's a good valuable member to the Justice League and the DCU mythos as a whole, but I don't like the Norse mythology bits.