Eli Roth's appearance in his debut feature, Cabin Fever, was a result of the original actor dropping out. But he clearly doesn't mind the bright lights shining in his eyes. Roth has had fun chewing up the scenery with brief appearances in many of his films since, including Hostel and Nicolás López's Aftershock, which Roth wrote, produced and stars in.
He's also played bit parts in the work of some of his fellow cameo-loving buddies, including Quentin Tarantino's Inglourious Basterds. Roth is personable enough to pull off a small scene here or there without ruining the movie; let's just hope he doesn't take any acting tips from QT.