I can't think of a complete list of five. Most films have at least some redeeming quality. But there are also so many stinkers it's hard to narrow it down to 5 (or even 10).
Anyway, one of the worst in my relatively recent memory:
Punch Drunk Love
Unlike TwinTurboJay, I knew going in that it wasn't a comedy (or at least I suspect TwinTurboJay didn't know it was a movie along the lines of the classics like "Mr. Deeds" and "Little Nicky"). I knew full well it was an art-sy fart-sy movie.
But I didn't know it would be absurd tripe.
To me it was as though Albert Camus came back from the dead, became a moviemaker, and made this turd. Supposedly a very "deep" film, I came away with the impression it wasn't about anything at all. Rather, it was boring and dumb, much like a lot of Camus' work.
L'Étranger immediately came to mind (to be fair it's the only Camus novel I've really given a lot of time and effort into reading thoroughly, so maybe not everything he wrote was crap, just the few of his works that I have read).
Then again, I've been accused of not being a particularly deep thinker. Maybe if a was a French homosexual
artiste living in a Paris (trying to think of the most stereotypical "artistic" or "cultured" person; no offence to homosexuals, artists, the French/Parisiens, or a combination of more than one of these things) I would have "gotten it". But, being your average North American schmuck, I didn't "get it".