It seems Douglas Adams preferred to use “Belgium” as a swear word (“actually the most offensive word in the universe“) after its U.S. editor forced him to change the reference to “A Rory award tor the most gratuitous use of the word ‘fuck’ in a serious screenplay“.

In the 2005 movie, “Belgium” is used a few times:

 

NARRATOR: “The best drink in existence is the Pan-Galactic Gargle Blaster, the effect of which is like having your brains smashed out by a slice of lemon wrapped round a large gold brick.”
ROCKWELL: “Belgium. Hold it one second.”
PERFECT: “Belgium”
ROCKWELL: “Ape-man, Earth dude, sorry, what’s your name again?”

 

PERFECT: “Hey, what did I miss?
DENT: “What have you been doing?
PERFECT: “Field research. So they found where we are? Belgium bummer!”

 

Franky MOUSE: “Shoot him, quickly, shoot him!”
Benji MOUSE: “Oh, bollocks!”
ROCKWELL: “Agghh! I’m gonna be sick.”
PERFECT: “Belgium.”