Well, since I'm a Monster and a Britney stan, there are really no more REALLY annoying fan bases out there besides them, to be honest.
But if I had to choose, it would be Rihanna's fan base. Over-hyping how much of a global superstar she is when her latest song was barely able to pass the 1 million mark in sales being number 2 on Radio Songs and her latest effort selling only 3 million WW with a huge single like WFL.
