The original motion picture. It's not the best outing, but it certainly doesn't deserve heat it gets
Darmok. It amazes me how many people get hung up on the minutia, and overlook the creativity and spirit of the Trek concept involved. Great Star Trek it is.
There are people who hate Darmok
Anyhoo, if we're speaking in terms of vitriolic, unreasoning hatred:
Movie: Star Trek V: TFF
Episode: The Royale (TNG)
Character(s): Dr. Pulaski, Wesley Crusher