When Neptune rhetorically asks Mindy why his crown is important, Mindy guesses it's to cover up his bald spot. He insists that he's not bald, just...thinning, and that the crown is a symbol of authority.
Neptune: Someday, you will wear this crown.
Mindy:(horrified) I'm gonna be bald!?
Three words. The Waiter Scene.
Spongebob: (is drunk on icecream) "Alright folks, this one goes out to my two bestest friends in the whole world! Patrick and this big peanut guy! It's a little diddy called, WAAIIIIITER!!!" (falls over)
The morning after. Oh dear GOD, the morning after. SpongeBob wakes up on the floor of Goofy Goober's Ice Cream Party Boat, which is now a complete wreck. The guy clearly has a hangover, his slurred speech and drunken behaviour are a hilarity to watch. Especially when he angrily remembers about Mr Krabs not promoting him to Manager, and when he notices Patrick unconscious under a table - Tom Kenny's delivery of this line is PERFECT:
SpongeBob later shows up at the Krusty Krab 2, where King Neptune has just arrived accusing Mr Krabs of stealing his crown. Still hungover (and mistaking the KING for a woman), he tells off Mr Krabs for thinking that he's still a kid:
SpongeBob:(belch) I'VE got somethin' ta say about Mr...(holds back vomit) Kraaabs!
Mr Krabs: SpongeBob, me boy! You've come just in time! Please, tell King Neptune all about me.
SpongeBob: I have worked for Mr Krabs for ma-many years, and always thought he was a great boss!
Mr Krabs:(to King Neptune) You see? A great boss!
SpongeBob: I NOW realise that he's a GREAT BIG JERK!!!(Mr Krabs turns to him, shell-shocked) I DESERVED THAT MANAGER'S JOB! Butyoudidn'tgiveittome! Because you said I'mma...KID! Well I am one hundred per-cent MAAAN! And this MAAAN has got somethin' ta saaay to yoooouuuu! (blows gigantic raspberry, then smiles smugly) THERE! I think I made my point!
"He's making a humorous diorama of... ALEXANDER CLAM BELL!"
"All bubble blowing babies will be beaten senseless by all able-bodied patrons in the bar"
The faces Spongebob and Patrick make during certain points in the film, like when they discover the Patty Wagon at the tough guy bar or when the monster in the trench swallows the "ice cream monster".
"Did you see my butt?"
Patrick: Did you see my underwear?
Mindy: No, Patrick.
Patrick: (holding shorts) Did you want to?
"So...you think I'm...stalling?"
The scream Neptune makes when he finds out that his crown is in Shell City:
Neptune: MY CROWN IS IN THE FORBIDDEN SHELL CITY!?
"WHERE AM I, IN CRAZYTOWN?!" An interview revealed that this was Neptune's VA Jeffrey Tambor's favorite line in the movie.
The "baby hunt" scene. After one of the testosterone-poisoned thugs finds a bubble from the aforementioned "bubble party", he makes everyone line up and starts playing the Goofy Goober song to weed out the "babies" (because "no baby can resist singing along" to the Goober theme). He gets to Patrick and Spongebob, and starts applying the nails by singing a few lyrics in a menacing tone. Finally, they can't take it, open their mouths... and a pair of Siamese-twins bust out instead, causing them to get beaten up.
"Oh! Oh! Wait! I want to make a distraction!"
Then: "I have to use the bathroom."
Though SpongeBob and Patrick's "death" scene is very sad, there is one funny part.
SpongeBob: Well, it looks like what everybody said about us is true, Patrick.
Patrick: You mean that we're attractive?
The sadness is lightened a bit when it cuts to the audience and every single pirate is bawling their eyes out, until the captain's parrot (not Potty, but sounds just like him) points out that they're missing something important.
Parrot: Awwk, shut up and look at the screen!
"GOOFY GOOBER ICE-CREAM PARTY BOAT!!!"
Spongebob: We're gonna party till we're purple!
Patrick:I LOVE BEING PURPLE!!!
David Hasselhoff coming out of nowhere to bring Spongebob and Patrick back to Bikini Bottom.
It gets even funnier in his last scene, after he succeeds in returning them home:
David: (Happily floating in the sea on his back, hands behind his head) Ya done good, Hasselhoff. Ya done- (accidentally gets blasted by King Neptune's fire) ...Ow.