Your friend sounds pretty sadistic.
I've seen a lot of movies....a lot..... so many that it's hard to pick just one. And there's so many different types of bad movies: like Longo pointed out there's post-2009 Adam Sandler movies, chick flicks, Michael 'Spolsion Bay, Put Shia in it, So Bad it's Good, Even More Found Footage Horror, torture porn, comedy sequels nobody asked for, etc etc etc
But if I had to pick one..... just one...
It would be.
I saw this as a young child and I remember hating it. And I was a pretty easy kid to fool when it came to bad movies. I loved Street Fighter, I loved TMNT 2, I just loved seeing my favorite things on the big screen. But Super Mario?? I actually left the theater so disappointed I was depressed. Yes this film resulted in depression for one of the happiest kids alive.
Let's also remember this is the first movie based on a video game. This movie set the trend for video games to be adapted into shitty movies. Hollywood execs would now sink their greedy teeth into the video game industry to produce films that were so bad they would eventually be given to Uwe Boll.
Fuck you super Mario Bros movie. Fuck you!