The mugger waiting at Korben's door is none other than Gothika 's and La Haine 's french filmmaker Mathieu Kassovitz.
Zorg's hapless assistant Right Arm (who operates the cockroach bug and impersonates Korben at the spaceport) is UK trip-hop artist Tricky. To be fair, Tricky's appearance is more like Hey, It's That Guy! than The Cameo, especially given he lasted half the movie.
The Mangalores' human disguises (and a lot of extras) are played by fashion models who worked with costume designer Jean-Paul Gaultier.
Fog, the nervous, stammering bellboy, is played by British stand-up comedian/occasional actor Lee Evans.
The larger of the two cops getting their lunch at McDonald's is played by Mac McDonald, well known (in the UK, at least) for playing Captain Frank Hollister, the ranking officer in charge of Red Dwarf.
Dungeonmaster's Girlfriend: Double Subverted. Besson wanted his girlfriend to play Diva Plavalaguna, but she initially refused because she didn't want to complicate their relationship. It was only when the actress they hired backed out that she agreed.
Enforced Method Acting: The wonder on Bruce Willis' face when the diva sings is real. That was the first time he'd heard it.
When Korban first meets Leeloo and she starts talking to him in her language, Luc Besson didn't tell Bruce Willis what Milla Jovovich was going to say to him, so Bruce's reactions are real.
What Could Have Been: Alert film buffs will note that Korben and Zorg never meet each other face to face. In an original draft of the script, Zorg would have faced Korben during the hotel evacuation, where the latter beat the crap out of the former for firing him and attacking Leeloo before stealing his ship (the ZF-1 was out of ammo). Zorg then survives the destruction of the hotel with the personal shield of the ZF-1, only to land in a massive glacier. He then calls his secretary to send another ship, only for the battery in his ZF-1 phone to fail.
Korben's mother is uncredited, but speculated to be Jill Mullan