Twice.
And it's no coincidence the same awful professor taught both classes.
First class I re-took with a different teacher and got a C+.
Second class, only this moron ever teaches it and it's a requirement for graduation. Since I had two Fs from one teacher, an otherwise spotless academic record (B was my lowest grade in any class prior to this), and the teacher didn't have much to back up his grades, they "generously" allowed be to take a D if I passed a takehome exam, in exchange for approving me to take another class this same bozo only teaches at another university, at my expense.
This experience is by and large the foundation of my belief that the US higher education system is flawed.