My mom and I argue over this sentiment quite a bit—she thinks Will Ferrell is funny, but can only handle him in small doses. For example, she's never seen Step Brothers in its entirety. I, on the other hand, have seen Step Brothers anywhere from 100-150 times. In fact, gun to my head, I could probably quote a fast majority of Ferrell's lines in the 2008 classic.
I do understand that Will Ferrell's brand of humor isn't for everyone! I just happen to think anyone who doesn't find him funny, doesn't have a sense of humor themselves. I'm sorry—strong opinions when it comes to this stuff, I know. Ultimately, no matter how depraved, every movie he appears in is made all the more comical by him just standing there, let alone speaking. See for yourself—
Personally speaking, my favorite on the list is a toss up between, you guessed it, Step Brothers and Talladega Nights: The Ballad of Ricky Bobby. For anyone who isn't aware, Ferrell's role in Stranger Than Fiction is actually a more serious one, but he's still kickass nonetheless.