Let's get the very first reason Nicki is hip-hop's most-hated out of the way first: She's a successful woman. This much should be obvious. There are a lot of people out there who have zero time for female rappers, even if they have to couch it in criticisms of her appearance from the left (promotes unrealistic images to women!) or right (slut!), her use of over-the-top accents, or her decision to pay attention to her pop audience (as if her hip-hop supporters were keeping the lights on).
This isn't to say that some criticisms aren't legitimate; her career isn't flawless. But it's tough to imagine that anyone else in the industry would be put under the relentless microscope treatment Nicki has received in the past few years.