While his trip is funny enough, the real hilarity comes whenever it cuts back to what's really happening. In one shot, Jack is singing inanely (with no backing band) while climbing up a tree. In another, he's being swept by raging rapids without a care in the world.
Cripple: Now come over here...so I can cut you.
Kage: ...no, dude.
Cripple: Fine. Then stay there...so I can cut you. (starts shuffling forward)
Jables:(to Kage) Dude, this guy's totally slow, we can totally outrun him.
They run. A little later, police arrive in response to the theft of the pick
Cripple:Catch me if you can!
They do so effortlessly
The Bong of destiny.
"I need a tight compadre who can teach me how to rock/My father thinks your evil, but he can suck a cock"
Almost every single word out of the Devil's mouth.
"You guys are fucking LAME!"
The first verse of "Master Exploder"
I do not need! (He does not need...)
A microphone! (A microphone!)
My voice is FUCKIN'! (Fuckin!)
After JB and KG's near-breakup after KG is exposed as a fraud, Lee, who has been off camera for most of the incident, reveals that he's been there the whole time and looks upon their matching ass birthmarks in wonderment:
Lee:You guys... look!
Ben Stiller's hammy performance as the music store clerk. Especially when he lights a match in the dark room and dramatically makes a Title Drop, followed by KG turning on the lights.
As in the show, Lee is a massive fan and loves Tenacious D about a hundred times more than anyone around him. During "History", while the rest of the patrons are either somewhat into it or completely unimpressed, Lee can be see shaking his head in disbelief of how awesome they are.
The break-in to the Rock and Roll History Museum. Jables thinks he's being a ninja, then we cut to him showing up on every security camera. The reason he isn't caught immediately? The security guards are too busy sharing blatantly false tales of their badassary while passing around a joint.
The contrived situation that puts Jables at waist height to a laser shutdown button but unable to move. KG, advises on a Chekhov's Skill from earlier: "The cock... use... the cock." What makes this is that he says it in a dramatic Mentor Archetype voice.