4. Australians - Django Unchained
Maybe "ruined" is too strong a word in this case, but by the time I got to the "Australian" scene in Quentin Tarantino's spaghetti western
Django Unchained, I felt altogether exhausted, and realising that - oh, God - Tarantino himself was about do attempt some "acting" - with an awful Australian accent, no less - just proved to be the last straw. The scene in question is the one where Django is being shipped off to work for a mining company and tries to convince his captors to let him go free. I don't know: this scene was just way too much, and was the first time I found myself thinking, "Oh, c'mon, Tarantino - rein it in, buddy." And yet this exists, and presumably only to play to Tarantino's ego. I don't mind directors making brief appearances in their movies, but a fully-fledged cameo with dialogue and everything... it's distracting as hell. In this case, the absorption is lost in the process of whatever is supposed to be going on here - and you don't really get it back after that.
Django is great up 'til this point, of course, but after you've heard Tarantino say "mate" a bunch of times, it's hard to get back into the movie.