“We have places your family can hide in peace and security: Cape Fear, Terror Lake, New Horrorfield, Screamville.” – FBI Agent
“Ohh, Ice Cream Ville!” – Homer Simpson
“No, Screamville.” – FBI Agent

Like a lot of Zombie Simpsons episodes this season, there is more than one Simpsons episode to which I can compare “Donnie Fatso”.  As has been pointed out in comments, the similarity to “The Trouble with Trillions” is uncanny, and not in a good way.  There’s also the epic fail of Homer’s catchphrase toupee camera, something that the hat from “Homer and Apu” would consider far beneath it.  For my money though, the most damning comparison is Homer’s previous interaction with FBI agents in “Cape Feare”. 

“Donnie Fatso” has a ton of problems, and many of those have to do with the rather serious way it takes its idiotic premise.  Agent Don Draper walks and talks like a straight ahead FBI agent, yet what he’s doing is unfathomably stupid.  Worse, it works; his brain dead idea to use Homer as an undercover agent actually gets Fat Tony.  Instead of using his foolishness for comedy, to show how bad he is at his job, he wins.  Inspector Clouseau and Frank Drebin won too, but they won despite their foibles, not because of them.  Of course, Clouseau and Drebin also had stories, which Agent Draper clearly does not. 

Contrast that with the Comedy 101 of the Witness Relocation Program agents in “Cape Feare”.  They’re playing the straight men to Homer, whose stupidity – as sincere as it is unrelenting – manages to fluster even the the kind of FBI guys who are so clean cut that they never leave the house until their shoes shine like mirrors and every hair has been carefully put in its place.  None of which means the agents themselves aren’t funny.  The list of what surely must be the most horrifyingly named cities in America would be good on its own, but it’s honed into genius level comedy by the dry, perfectly even delivery of a man who not only isn’t in on the joke, but may not be aware of the existence of humor.

Agent Draper is like that too, but he’s never given anything nearly as absurd to say.  Instead, his investigation plods monotonously forward in spite of itself.  Even this doesn’t really elicit a reaction, humorous or otherwise.  Here he is when we first meet him:

And here he is later, after Homer has infiltrated Fat Tony’s organization:

Finally, here he is when we last see him:

Notice a difference?  I sure don’t.  He certainly doesn’t look like a character who just went through any kind of story.  Of course, that’s because he didn’t go through any kind of story.  He was just a prop, a one dimensional set piece so that Zombie Simpsons could put its star attraction into a half assed mob plot. 

Compare that with the agents from “Cape Feare”:

Here they are when we first meet them, forthright, button down Bureau men straight from central casting: dark suits, tightly knotted ties, no nonsense expressions.  Here they are a mere minute and a half of screen time later:

Even without the dialogue you can tell exactly what’s happening.  The agents have taken off their jackets, their sleeves are rolled up, and their ties are loosened; the ashtray is full of cigarette butts.  The guy on the right even has a coffee mug so we know they’ve been there awhile.  The straight men have been broken by Homer.  Even better, he did it completely unintentionally.  No crazy outbursts were needed, no screaming, no megalomaniacal declarations.  Their brief, nameless appearance has far more personality and comedy than the dried out windbag Zombie Simpsons used as an excuse to let Homer kick, scream, cry, and generally freak the fuck out for most of an episode.