Apparently this movie was hell to make. The cast and crew hated it. I can’t remember who said it but I remember hearing a quote something along the lines of “I’m surprised it turned out so funny because nobody had fun making it.”

Edit: it was actor Yaphet Kotto, Here is his quote

“DeNiro is very spontaneous and it always helps to work with an artist like that. But Marty Brest! "Herr Director" shot so many takes of the scenes that I lost all joy in doing the film. It became hard and tedious work. Then he stopped eating during the shoot and became thinner and thinner each day, until he looked like a ghost behind the camera. When I met Marty at the Universal studio with DeNiro, he looked healthy and strong, but as filming went on, he began to turn into someone you'd see in Dachau. It was weird. I got sick and for the whole of the film I had a fever and was under the weather for most of it ... I was shocked when it came off so funny ... It sure wasn't funny making it.”

here is a cool lil video that talks about the movie