The single worst movie I have ever seen in my entire life was
Troll 2. It has actually become well-known on YouTube as being the worst movie in existence.
I think they should take it a step further an officially make it the worst movie ever made. On the good side, at least now I can literally watch any other movie and, no matter how bad it is, say "I've seen worse".
Seriously, just go on YouTube and type in "Troll 2" and watch anything that comes up. You will ask "wtf" thousands of times in your head, or aloud if you feel you have to.