This is one of the few Family Guy episodes without any secondary or sub-plots, and it did adequately well for itself for the first two acts.  Unfortunately the plot collapsed in the third act, and the episode as a whole compares unfavorably with similar episodes on other shows.  But overall, it was certainly watchable enough.

The question this episode seeks to answer is, "Where do dirty jokes come from?"  It's a good question, and they could have taken the answer in a lot of different directions.  It all starts with a dirty joke so funny that Peter poops his pants every time he hears the punchline.  Soon, Peter, Joe, and Quagmire are tracking down the answer, through a convoluted string of players.

You could make the answer just about anything, actually, from an underground empire of squid monsters to the collective unconscious filtered through a coma patient.  See?  I just came up with two better answers off the top of my head, right there.

In tracking down the answer, the Quahog trio meet up with Cleveland in a cross-over.  As Peter says, "Holy crap!  Who knew we'd run into you here, except everyone, 'cause Fox ruined it in the promos."  Cleveland's participation turns out to be completely unnecessary, leaving me to wonder why they bothered crossing over at all.  

I kept thinking about the American Dad episode where Steve tracks down Mr. Peanut, and the Simpsons episode where Homer joins the Stonecutters.  ("Who keeps the metric system down?  We do!  We do!")  Both of those episodes were wacky and inventive, and if they were exceptionally silly in some parts, there are certainly worse things in the world.  Like boring.  At least those episodes weren't boring.

Unfortunately it turns out that all the world's dirty jokes come from a secret island stocked with very smart men.  That's pretty weak, if you ask me.  For one thing, why are they doing it?  Who finances their operation?  The thing about dirty jokes is that they are a currency which trades for free.  There's some interesting stuff you could say about that, but Family Guy fails to say it.

I haven't even mentioned the casual misogyny and racism.  Is this really the same show where the characters are occasionally shocked by Brian's racism (which he blames on his father)?  The "would you rather" during their long car trip made me:

A) wonder if this was just a different category of gross-out joke, and

B) long for the scene where the entire Griffin family sings "The Rose" (a.k.a. "Some Say Love") as a driving song in the episode "Baby Not On Board."

As entertaining as the first two acts are (even Bender from Futurama makes a guest appearance!) the third act is a straightforward action sequence.  Blah.  And an entire road trip episode without a single musical number?  Even Chris managed to work in a George Michael routine when he was stranded on a desert island.  For shame.  

I know it's trite to say "this show is really going downhill," but sometimes I have to wonder.