Among serious contenders for the title of Worst Movie of All Time, the winner in the Sci-Fi Musical genre is without any doubt Menahem Golan's masterpiece The Apple. In fact, it is hard to see how this film could be made any worse, so much attention is given to screwing up every detail, the plot, the music, the set decorations, the acting, and really everything else. Set in the USA in 1994 and filmed around 1980 in Berlin, Germany, this is highly concentrated trashy euro-disco aesthetics, although the music borrows heavily (and ineptly) from other genres like reggae, hip-hop, soul, etc. Here are the first 6 minutes, featuring the song "BIM".
You can download this video in higher quality here [ 44 meg MP4 ]. To get an idea of the horrors of the rest of the film, check out the trailer on YouTube. You can even get the whole thing on DVD at Amazon. By the way, George Clinton co-wrote the lyrics for the songs in The Apple.