I've seen a couple over the years: Robin Hood, Twelve Chairs, Blazing Saddles, and most recently Spaceballs. I found them all funny, theoretically, but they rarely got an open laugh out of me. It seems like most of the time this is just because the comedic timing makes every joke or funny bit land very awkwardly, or with just a bit too much space to leave room for any subtlety or reward for the watcher.
I feel like I remember the few I saw as a kid being funnier at that time. Is it just because my brain has been attention-poisoned with the rapid fire wit of modern comedic television?
I've always heard it told that he was in fact not told the punchline before filming and was just told to try and not laugh no matter what.