Draco in Leather Pants: The Gill-man often gets painted as a misunderstood romantic, unfairly provoked by the human characters. While the character is intended to be somewhat nuanced, he still kills two guys with zero provocation at the start of the film and his kidnapping of Kay is very non-consensual on her part.
Fan-Preferred Couple: Officially, Kay's Love Interest is David. But many fans sympathetic to the Gill-man's plight prefer she would return Gill-man's love instead despite the fact that Gill-man kidnapped Kay against her own will. A short-lived 2009 musical adaptation in Universal Studios even made this fan preference central to its version of the story, with Kay rejecting David in favor of Gill-man only to be then unwittingly eaten by him. This is ultimately what led to the creation of Guillermo del Toro's The Shape of Water, as he wanted to make a movie where Gill-man and Kay do get together.
First Installment Wins: While the first movie is considered a horror classic, the two sequels are not nearly as well known and generally agreed to lack the charm of the original.
Ho Yay: Between David and Mark. You'd think there was something there that David didn't want Kay to know about...
I Am Not Shazam: The monster is never actually referred to as "Creature from the Black Lagoon". He's called "the Creature" a few times, but never the full title. His official name, especially in the second movie, is "Gill-man".
Nightmare Retardant: Posters for the film developed an odd tendency to depict Gill-man with a pair of clownish red lips.
Strawman Has a Point: Mark may be a Jerkass, but if they'd listened to him, they'd have wound up a lot better: If they'd killed the monster (who they knew had killed at least four people previously, at least 2 without provocation) they'd have been fine. If they'd have left when he wanted to, rather than taking pictures of the cave then the monster probably wouldn't have broken out. And if he hadn't gone underwater after David, then David would have almost certainly died (although this last one was done out of purely ambitious reasons and no actual caution).
While the bonus multipliers are displayed as 2X, 4X, 6X, 8X, and 10X, in reality they are 2X, 4X, 8X, 16X, and 32X respectively. Custom ROMs fix this, but also make the bonus far more substantial despite the lower multipliers.
The Snack Attack hurry-up underflow glitch can lead to scores near the Cap of 9,999,999,990. The hurry-up will sometimes wrap around to a value very close to that cap. A player with a low enough score can intentionally let the hurry-up run long enough so that collecting it will not make his score exceed that cap, and have a nigh-unbeatable high score.
