A snorkel folded up in a BC pocket is just as good as one on your mask strap in a true emergency.
A pony bottle will cause you to never pay attention to your primary air supply.
A crotch strap over a weightbelt could never cause a problem
An 80 cu-ft tank can never be used deeper than 120 feet or you will die!
Ditching lead at depth (any amount of lead) invariably causes the diver to rocket to the surface uncontrollably.
The only place you ever want to drop lead is on the surface.
Sharks are only curious, they do not view a person as food and will never bite a diver as long as you are calm.
You must enter the water with air in your BC and signal to the operator that you are OK and then you must descend feet first.
Freedive fins do not work for scuba diving because.....hmmm.. I forget why... but it is just one of those things...
If you are a good buddy diver, you will never have a problem with getting air from your buddy in an emergency, thus carrying a pony bottle is an unnecessary crutch that demosntrates that you do not have good buddy skills.
Wearing a bunch of guages on your wrist (rather than a console) is always best.. even when reaching into dark holes and yanking lobsters.
You are not much. much more likely to die in your first 20 dives than at any other time in your dive career.
There is no reason to wear a hood if the water is over 72 degrees and trigger fish will never bite off portions of your ears.
It is impossible to chip your front teeth by clutching a grouper.
Suicide clips are fine as long as you don't do penetration dives in wrecks.
A BP/W is configured perfectly. it places the bouyant cell above the diver's body and this makes maintenance of a horizontal and steamlined position effortless while submerged. However once the diver reaches the surface, the bouyant cell located above and behind the diver no longer serves to hold the diver in a face down horizontal position. At the surface, it now holds them vertically and comfortably in the water column with zero effort. Engineers can be easily explain this phenomenon by use of a static force diagram showing bouyancy and gravitational forces.
A BP/W harness with no padding, no adjustability, stiff nylon belts and a metal plate pressing on your back is infinitely more comfortable (while walking from the car to the water) than a padded BC harness with adjustable shoulder straps.
It really is important to be able to swim backwards when diving. All the marine mamals swim backwards effortlessly, in fact many Orcas swim backwards 90% of the time (but only in the southern hemisphere).
It would be incredibly irresponsible to work on your own scuba gear. It is infinitly safer to trust some shop monkey who gets paid less than your garbage man to work on the stuff.
You can buy a reasonably well made pneumatic tool, such as a grinder for $15 at Harbor Freight, but unless you spend $800 for a scuba regulator the thing will not work.
The best thing to do for your buddy when they have a freeflow is to turn their only source of air supply off (so they don't loose their air supply).
A one-way (purge valve) on a snorkel is a dangerous and superfuous component to use at the surface when snorkeling, but the EXACT same device functions flawlessly in the second stage of a scuba regulator at 200 feet.
Pissing in your wetsuit is bad form if you have not yet entered the water.