OK, you sit yourself through a watchably mediocre or outright awful film, but there's a genuinely redeemable and entertaining aspect to it. In regards to the slightly tacky and bland 1997 remake of the 1960s The Day of the Jackal, called The Jackal, the one main thing going for it is MVD Major Valentina Koslova played by Diane Venora. Resourceful, loyal, attractive, and mysterious, on hindsight I'd rather wanted The Jackal to be more about her fighting the Russian Mafia alongside the FBI liaison agent played by Sidney Poiter, instead of the movie being a generic ego vehicle for Bruce Willis and Richard Gere that has a script that heavily borrows from (by most accounts) a better movie. And Diane Venora's is so good they just had to bump her off in a horrible way (that left me feeling annoyed and legitimately saddened). What other examples are there?
More guilty pleasure than pure crap, but I really like Russell Crowe and Lucy Liu's characters in The Man With The Iron Fists.
Sam Elliot as General "Thunderbolt" Ross was the only watchable thing about that crap Ang lee Hulk movie.
Alan Rickman as the Sheriff in the otherwise dreadful Costner Robin Hood. eta: Morgan Freeman's character in the "just OK" Now You See Me.