The hubris of zooming around Poseidon's domain like it owned the place
Forgot to pack short grain rice, soy sauce, rice vinegar, and Wasabi. Hope you like seaweed for dinner, boys!
Captain is a self-professed loner, has a mode of travel that requires dozens of crew in close proximity.
Definitely smelled musty in there.
20,000 leagues was the distance they traveled, depth rating was probably nothing special.

spoiler for a 200 year old book

Couldn't even handle one measly whirlpool, probably would've performed awful in a hot tub

Most importantly: shared a name with the worst animal in the ocean. Terrible choice.