You mentioned checking the spg of your buddy which is good. This is probably the wrong mindset for me to have (I KNOW it's the wrong mindset) but oftentimes I feel like it's a little of an insult to have someone checking my stuff before I get in. Wrongly, I suppose, I usually want to say "look twit, I'm not incompetent" but I never say it, I'm polite, believe it or not.
I'll admit that the crew I dive with are mostly tech divers and what I consider very, very good ones at that. Rarely do we do buddy checks. We kit up, jump in, figure out if everyone is squared away then down we go. However, I usually give a good visual for everyone in my general vicinity for bubbles or any other anomalous situation as we descend.
If I'm diving with someone other than the usual crew I check a few things on them like hoses connected, air on, and check inflation and regs to be working. Sorry for being off topic.. END OF HIJACK.
But again, as far as me, I always, always check breathing things, spg, and inflation at waters edge or on the back of the boat, and
always immediately prior to entering the water. If I have air and inflation then I can handle anything else I may have forgotten. (like zipping drysuit closed fully! LoL)
I check my air upon setting up gear, and then just before entry I check it again after taking two breaths from the reg. Sometimes air can be turned off and you can get a breath from the hose. I also always check my buddy's air. I don't ask. I do it , and show them mine. When I am working as a DM on the dive deck, I check everyone's air before they enter, by looking or having them look. In Hawaii I find it hard to imagine a crew member on a dive deck not doing this. We dive there alot.
DivemasterDennis