Sometimes, an unexpected cameo can elevate an otherwise solid movie into a genuine cult favorite. Matt Damon’s unhinged performance of “Scotty Doesn’t Know” is the most prominent thing I remember about 2004’s EuroTrip, as he belts out a punk-rock song about cuckolding poor Scotty. Bradley Cooper appearing as a charming little halfling with a fetish for burly barbarian women remains one of the funniest scenes in Dungeons & Dragons: Honor Among Thieves. And who can forget Bill Murray appearing as himself posing as one of the undead in Zombieland so he can golf in peace?