The best one was when I was having four impacted teeth removed. Local anaesthetic and laughing gas, so I was aware of what was happening during the whole procedure.
It was weird overall, because it was a fancy office where they let you watch a movie during the surgery. I picked "O Brother, Where Art Thou" but the headphones were only playing static. Of course, by the time they put the headphones in, it was too late for me to tell them anything, so I was watching a movie to the sound of them talking bullshit to each other, like who got how drunk at the last big party, gossiping about people they all knew, etc.
During this, because of the anaesthetic, I barely felt any pain, but could feel pressure, so I could feel them cutting through my teeth and rolling them out of my gums with pliers. Best part of the surgery was when I felt something splash out of my mouth, then head the dentist say "Why do these people always wear white?" Turned out to just be saliva, not that it mattered (I had purposely worn an old white t-shirt that I never wear in case it got blood on it).
Also, one of the assistants was one of my old public school classmates :/
Overall a pretty bizarre experience, but not something I would call unpleasant.