I saw Blazing Saddles way back in the day. Walked in cold, having no idea who Mel Brooks was (even though I had been a huge Get Smart fan). I laughed like never before - or since - in my life.
I also went in there cold (it was the middle of February!) and I'll never forget the non-stop laughter. We had to go see the movie a second time because we missed half the jokes, due to all the noise and laughter in the theater. The only other movie that came close to non-stop laughter like this was "Airplane" that came out about five years later. That's probably another movie that could never be made today.