"I have witnessed divers pulling out batteries, hanging computers in the water “to decompress,” and even leaving their PDC on the boat for a dive to “cool off.” None of this is a good idea. Seriously."
Until a couple of months ago, I would have hoped divers were smarter than this. But not any more.
Not only do people think that diving within the limit of a computer is completely safe, far too many assume that the comp has a massive safety margin built in, so it's OK to push the limits, or even break them.
In a recent series of dives on the President Coolidge in Vanuatu (to 40-69m on air, with ~50mins deco times) I witnessed a group of divers coming to the surface early after each dive, then throwing their comps back in the water on fishing line to "finish" the stop. When asked, they said "computers are too conservative" and they were bored (the deco stop was in a stunning coral garden with rainbow mantis shrimp, clownfish eggs spawning and the occasional dugong flyby - bored!!!). After a couple of days, one diver's comp went into violation anyway, and we saw him flipping the battery to glitch it out of violation. When it didn't work, he bullied a local dive guide to borrow a new comp for their last dive. To cap it off, one woman in the group wondered why she was getting headaches and bleeding from the nose and ears. This was on a full penetration wreck dive where there had been a fatality in the last few months.
After my wife (>400 dives DM) and I tried to talk to them about how dangerous this was to no avail, all we could do was insist that they dive well away from us. Not willing to risk ourselves in a rescue situation to save idiots.