That is a very hard question actually. What makes a game bad? Being broken, being not fun?
Being stupid?
I think that, for being a flagship title and a launch title, 1-2-Switch is probalby the most ridiculous and stupid game ever created, but does it make the worst? probably not.
I played the usual suspects, like ET - Atari, which is actually charming in a way and many other, like Dick Tracy - NES, which I actually like a lot.
So, if there is such a game, probably is buried in a Comodore 64 library or something and most of us never even touched.