In the category of useless/infuriating:
In uni there was a required class for CS majors called "Languages." The fucking thing was just "here's a bunch of weird-ass programming languages, learn them." I thought, OK, fine, at least it's online so I can stay home.
Semester starts. I log in expecting to see content and there's nothing. I message the prof and say, "Hey, I'm not seeing any lessons uploaded. Is this on my end?" An hour later I got a notification that there'd been a bunch of Powerpoint slides uploaded. Great. This goes on for weeks - someone has to message the fucking guy to get him to upload lessons, so at some point we stopped emailing him and hoped he'd just forget he was in charge of the class and get an easy A. That's exactly what happened. Occasionally he would realize he fucked up and would send out hurried emails claiming there'd be quizzes and tests over the lessons so far. Well, what lessons? The fucking Wikipedia-sourced Powerpoints? Nothing ever happened.
At my school, if a prof had an online class he/she was required to hold office hours each week. These were hours where they had to be on-campus to upload lessons and have in-person meetings with students. I eventually had this realization: If this dude is holding office hours each week for this class, what the fuck is he doing with that time if he isn't running the course?
Weeks later, after the class had completely stalled, I logged onto our school's social media platform during his "office hours" and saw it: "Women are better than men at programming". It was a link to an article and the absentee professor had posted it proudly with the caption: "Men, pay attention. A lot of you just don't have what it takes. We need more women and less men in this program." Within minutes the comments went nuclear. But instead of issuing an apology, backing up his arguments, or whatever, the guy says "What I've learned is that you're all sexist pigs." I screencapped immediately and cross-posted it to every comp-sci group on campus. Specifically, I linked it to every student who had his useless online class. He later went into DFE mode and denied it happened. Regardless, we never heard from him again and I got a nice, shiny A for doing jack shit.
Later I found out the professor had given As to everyone except the single female student, who he gave a C. She was a straight-A student and the C had thrown her graduation w/ some kind of honors into limbo.
That's right, Mr. "Women are better than men" gave the ONLY female student a C for a class he released zero gradeable assignments for. Fucking LMAO. She immediately contacted the higher-ups and nuked him from orbit.