I hate (in a more extreme sense) an anime if it looks like something i've seen before to the point that it becomes sort of a rip-off. Of course, the looks-something-like-*that anime* syndrome is common in anime-dom. But there is a big difference between look-alikes and blatant rip-offs. There are lots of similar shows out there, the mecha genre for example. They may have looked similar overall but they never fail(most of the time, but there are still lots of bad mecha shows out there) to show us something new without destroying the elements that iconographize their genre. However, there are shows that fail in this category, sure they follow the genre per se but they fail to give a sense of uniqueness.
Examples: Yu-Yu Hakusho(the GOOD)-Flame of recca(the BAD), Sailormoon(the GOOD)-most similar shows that tried to follow its footsteps(the BAD)...
Another thing that turns me off is bad art and poor animation considering the technological capabilities of its time and the artistic style. Budget is one thing but there's a thin line between making the BEST out of it and making the MOST.
Example: Gundam SEED, yes SEED coz i think it went over the top in how it was animationally and artistically executed-the characters only tho...IMO