When they replaced Tara with a shitty wannabe
The Tara-Willow pairing was the stuff relationship dreams are made of. They were perfect for each other, and perfect individually. Then Tara had to go and get herself murdered, and Willow had to lose her humanity, and then she had to rebound with Potential Slayer Kennedy. Unfortunately for everyone, Kennedy’s only personality trait seemed to be that she was an open lesbian. Ooh, hide your children.