I'll probably get some flak for saying this, but one of the worst films I've seen is Suckerpunch. Just really a bad excuse for hot girls and guns (not that I'm complaining at that bit in itself :lol ) but the portrayal of the characters was pretty dire, and the setting of a mental institution was a poor way to have girls "fighting the male power". To have attractive girls shown being mentally and emotionally vulnerable in a weird-ass mental home, whilst still attempting to sexualise them actually made me really uncomfortable. ASide from the misogynistic undertones, the dialogue and plot was terrible, the plot literally made no sense; like if they had a key that opened all the doors, why did they need fire to open all the doors; and if they didn't know that they were going to get caught, why did they actually need the knife?
Well anyway, the soundtrack and visuals were rather nice. I haven't seen many truly awful movies though...