The Kraken:
Believe it or not, FW, the frequency with which people will make shore dives without turning on their air is unbelievable!!!
Needless to say, this comes from poor buddy checks and pre-dive procedures and planning.
the Kraken
Happens to me when the wife is my buddy and turns my air off during the buddy check. She's a pistol, I tell you.
Others:
Forgetting weights.
Forgetting to inflate the BC on a boat entry.
Forgetting lights on a night dive or not having enough battery for the duration.
Failing to inflate the BC on the surface.
Free-flows
Not torqueing the tank band tightly enough
Blocking the gate
Being oblivious to other divers who would like to get past you and make their way to the gate
bc's mounted backwards
regulators mounted backwards
forgetting to tag your tank after a dive
gear spread hither and yon
gargantuan dive bags
walking with fins on deck
lights on mask straps/head/shoulder
blinding people with your light on the surface or U/W
not cleaning up after gutting your catch
rinsing gear in the camera tanks