WHEN I FIRST SAW Conan O'Brien in a film (South Park: Bigger, Longer, and Uncut) he was voiced by Brent Spiner, he jumped out of a window, and he died. This—and the new documentary Conan O'Brien Can't Stop (see review this issue)—puts him near the top of an exclusive list: "Mostly Not-Crappy Appearances by Talk Show Hosts in a Movie."

Jon Stewart's overachieving ass is on it twice: Once as the backstabber Marion Stokes in Death to Smoochy (2002) and again in the role of The Guy who Bagged Gillian Anderson in the Little-Seen Playing by Heart (1998).

David Letterman in 1994's Cabin Boy? Eh. I'll allow it. He sold fine monkeys.

Mention must be made of Ellen DeGeneres as ditzy Dory in Finding Nemo (2003)—a performance that almost made me understand why millions of people voluntarily tune into her every morning.

1988's Coming to America co-starred Arsenio Hall before he was a barking, triangle-headed threat to The Tonight Show, but Arsenio is, as always, second banana: He loses the top spot to Oprah, who got a Best Supporting Actress nomination for The Color Purple (1985), in which she played a strikingly defiant public urinator.

But this list has an opposite—one full of terrible, terrible appearances that make jumping out of a high-rise seem preferable: "It Ain't So Easy without a Desk, Huh?" 

Leading the charge with three appearances: Rosie O'Donnell, first as an undercover cop at a fetish resort in Exit to Eden (1994) before going on to portray an annoying ape in both Tarzan (1999) and A League of Their Own (1992).

While Jimmy Fallon can count a decent turn as the manager of Stillwater in 2000's Almost Famous, it's canceled out by his blank bumbling through 2004's Taxi, a wet fart of an action movie. And while George Lopez lent his voice to the frilly pink abomination that is Beverly Hills Chihuahua (2008), all these cinematic crimes are mere misdemeanors compared to 1989's Collision Course—a boring, unfunny, racist buddy-cop flick that reinforces a simple, universal truth: Jay Leno ruins everything.