Every time someone brings up a vacuum and mentions it not working I am 99.999% likely to make a ‘that sucks’ joke.  In which case its not funny, it is entirely predictable, but I can’t leave it alone.  It is like my daughters and the knock-knock jokes.  They tell the same joke over and over and yet its always funny.

Or why did the chicken cross the road?  Pretty much any answer will do, they just laugh and laugh.