Last year, in Key Largo, diving the Eagle.
I had gone out with another charter in the morning, as the one I was staying with wasn't going out that morning (conditions were marginal), and had two good dives. Went out that afternoon with the charter I was scheduled with (conditions had improved) and picked up an instabuddy. I should have known better, as he came with a large group and was the only one without a buddy.
I was using nitrox to lengthen my bottom time, and made it clear (I thought) to instabuddy that my max depth would be 102' (he was on air). We get to the eagle, and instabuddy drops immediately to the sand (~115'), with his console hanging around his ankles. He's completely oblivious, and takes off staying deep, while I'm above him at 100'. He cut through the wreck to the upcurrent side and into a ripping current.
While cutting through the wreck, he picked up some mono line that was still attached to the wreck and had a good sized hook headed straight for his hoses, so I broke my MOD and went down to get him. Pulled him up to 100' and untangled him (as we were pressed against the wreck from the current. Grabbed his gauges and looked: 700psi! (I still had 1800). Tried to get him back to the other side of the wreck, where we could get back to the mooring line, then share air, but instabuddy hand over hands the wreck back to the line and shoots straight up, passing several divers doing their safety stop.
When he hit the line, I initially tried to catch up with him, but realized that he was going waay too fast. At that point, it was bon voyage. Did a normal ascent and safety stop. Got back on the boat, and hunted him down before I even got my gear off, and asked "What the **** were you doing down there?" He replys "My air just disappeared. I don't know what happened". Then I started heaving (very unusual for me) and sprouted one of the worst headaches I've ever had.
Both the captain and DM came over and asked if I wanted O2, but declined, as I was pretty sure it was a CO2 hit from the exertion of freeing instabuddy from the mono.
I skipped the second dive, and went home a day early. Man was I ever pissed. He made the second dive and was headed back out the next morning while I was packing up.