I used to work with a chap who worked previously for Taunton Cider, it was when Leslie was doing TV adds with The Shadows for them.... He paid a visit to the works and meet the workers threre and was apparently a thoroughly nice chap.
I remember watching "Flying High" again when a whole heap of us kids had come home to visit Mum and Dad. Mum was in and out of the room (she rarely sat down) but we were laughing so she popped in now and again to look at the TV. She walked in just as the nun swings the guitar around and rips the drip out of the kids arm. We were falling around and Mum was shocked! "You find that funny do you!? That poor child! I am not stopping in here to watch this!" and stormed out; thoroughly disgusted in us all! (which made us laugh even more). Ever after when we saw that scene we would all get highly indignant at anyone who laughed and storm out.
I think Airplane was his first comic vehicle - up until that point he had always been a very serious actor. I think he quite enjoyed his comidic reputation after that.
Did you know his older brother Erik Neilsen was deputy prime minsiter of Canada for a while ?? He was nick-named 'Old zipper-lips" because he knew when to keep his mouth shut and never let slip any of the goverment's secrets.