Scenario #1 - The Speed Demon
What do you do ... and why?
I've gone through a similiar scenario with an instant buddy who darted from place to place without a thought to where that person was going, air consumption, touching animals and bouncing off the bottom, etc., then ran low on air.
I stuck with that person because I agreed to be that person's buddy FOR THAT DIVE. After the dive was over, I told that person that it looks like our styles of diving don't jive so we should find different buddies. I would not abandon a buddy unless that buddy is killing him/herself and probably take me with him/her if I were to stick around.
Scenario 2.
I had ONE certified dive under my belt and my buddy of 500+ dives decided to penetrate a small sailboat. It was nothing really, a tiny sailboat with nothing inside to trap you and a whole big enough for a freight train to go through. But it was a wreck penetration that we never planned for. He signaled me to follow him and I shook my head. He went in anyway. It scared the piss out of me because if something were to happen to him, I wouldn't know what to do except run for the surface and yell for help. This is the same buddy who kept on diving after we got separated a few times because he "trusted me and knew that I would have been OK". I was fresh out of freakin' OW class
Though I liked the guy, we stopped being buddies and I'm sure he was relieved not to have to put up with a newbie.
Later on, another instant buddy that I knew but never dived with before. This guy seemed to be a cautious diver (he had double redundancy for everything), and we're both seasoned enough to have some fun. Off we went and everything was great until he saw a crevice that seemed to have enough room to penetrate and he shined a light through to the otherside, apparently there's a pocket big enough to house a diver. Next thing I knew, he wriggled through the HOLE!!!
Didn't even give me a sign or anything, but went right into the rabbit hole. He then had the nerve to signal me through. I said HELL NO!!! We finished the dive and I asked him not to be my buddy again.
There are things that I refuse to participate in and impromtu penetration of overheaded environment without proper planning is one of them.