Administrators that think adjunct faculty are a good idea.
Dinosaur graybeards who maintain the status quo.
Faculty who haven't updated their teaching in fifteen years.
Faculty who won't admit academia and the research funding situation have changed dramatically, and continue to do so rapidly.
Faculty who only train future faculty.
Faculty who treat department staff like dirt.
Faculty who treat their lab personnel like dirt.
Postdocs who think they've got it all figured out.
Grad students who think a PhD is a given.
The third reviewer.
I've barely scratched the surface with the above. Go hog wild in the comments.