I've had a few awful teachers or professors over the years. One professor that sticks out was a total asshole to me. I had to go for surgery and rehab on an injury, so missed two of his classes. I emailed ahead to ask if there was anything important covered that I should make sure to read about in the required text, and his response was "this is an ignorant comment, everything I teach is important, if this is your attitude you're going to fail". The man was such a cunt that 16 years later I still use his work and personal email address (note: don't put your personal email in your book that every student is forced to read for your shitty intro class) as spam fodder whenever a dodgy website has a subscription or email box.

Pair that with another professor, who gave an assignment with tiers for extra credit, on the basis that you complete the first tier to be eligible for the second. I decided to go for full marks, and completed all tiers, but broke my code 10 mins before review. He reviewed, told me that it was great that I even attempted, and only marked me down for the case I failed - turning a potential zero into 90%. It was the final mark I needed to pass his class, complete my degree, and to get the prerequisite to join my masters degree programme.