It is odd - I have a friend who never gets the joke. If I tell him a joke I have to preface it with the word "joke". He doesn't seem to get irony or sarcasm either.
(but he does find "Mrs Brown's Boys" funny - which I don't at all!)
Dave, I have a friend like that. Never gets anything I say that I think is funny or a joke, yet she loves Mrs Browns Boys and even went to see the show when it was doing the rounds.:-(
Must admit I only have 1 friend whose sense of humour is exactly the same as mine and this is one of the reasons we've been friends since our first day of school.