to the op.....
i applaud the fact that you are taking this seriously. i also think your choice of title for this post is good one. "embarrassment" is a very powerful emotion. people have actually died because they are too embarrassed to go to the hospital for example when they have symptoms of a heart attack.
as divers (and especially as male divers) we don't need anyones help. we are more than capable of doing things ourselves. and agreeing to do something as silly as a pre dive briefing or a quick bubble check is for weak people who don't know how to really dive. (can you hear the sarcasm?)
you really have three choices when diving with someone. you either decide you are ok with them skipping steps you believe to be important (what happens after that is now on you), you dive with someone else, or you dive solo. it really is that simple. make the choice. don't just go along with the herd.
people seem to loose site of the fact that if your buddy misses a key step in the gear assembly, or does not understand the dive plan / gas plan, or basic communication, that it can put you in harms way as well. it is not just about them. thats why we call them a "buddy". you are supposed to work together whichs helps reduce the chance of something being missed. thats the whole point.
if we are all so self sufficient then we should all just dive solo (which is perfectly fine in some cases if done properly). just be honest with the diver you may get buddied with and let them know you are not interested in being a buddy.
i had a "buddy" that i was paired with in cozumel once. she was someone i never met. she lived on the island and apparently had a bunch of experience. once we hit the water, she took off and i never saw her again until i was back on the boat. nice.
that said, you cannot put a gun to someones head and force them to do it the way you feel it should be done. thats when you need to decide whether you are comfortable diving with them or not.
i will add a comment about a topic brought up a number of times in this thread. that is about checking to ensure the gas supply is on before taking the plunge.
i too have had dive guides / boat crew turn off my valve. i prefer to handle all my own gear and discourage anyone from actually touching my equip. pointing something out that looks incorrect is just fine but pls keep your hands off.
i teach my students that the final thing they do before entering the water (after doing all the other standard checks) is to look at their pressure gauge, take two breaths, and watch the needle. it should indicate full pressure and should not move. if it drops to zero or close to it, the tank is off. if it drops slightly when taking a breath, the valve may be only partially open or faulty. i have seen more than one diver on a boat jump in and come gasping to the surface because they have no gas.
i have never had a problem diving with people i know. i assume because we are more comfortable than we would be with a stanger. most of the resistance seems to come from people i don't know. this can either be from embarrassment and / or ego, they were trained differently, they just don't know any better, or are simply complacent and lazy.
it only takes a minute to look over your buddies gear (they may not even realize you are doing it), check that both of you have proven your gas is on, and even do a simple bubble check at the surface. there simply is no reason not to do it.
i have seen people jump in with no mask, no fins, (one guy had no mask or fins) no gas on, bc inflate not connected, drysuit not connected (i seem to do this more than i should lol), bc hose behind them, mask skirt over their hood, octo hose wrapped around another hose, octo not secured and stuck behind them, etc etc.
i even jumped in once and had not secured my tank band. haha go figure. we also had a buddy that was ready to jump in and noticed a slight hissing sound before he did. after a gentle wiggle of his hoses to see if one was loose and leaking, one hose blew right off. it came apart. had we not noticed, that would have been a serious problem on the wreck at 110 feet.
i hear the same thing over and over......"i have been diving 50 years and nothing bad ever happened to me". well good for you. you may have never discussed a dive plan. never made a gas plan. never had an equip failure. never had a panic attack. never got separated. never delt with an out of gas situation etc etc. and the answer is still the same. it is never a problem, until it is. those of us that have either experienced some of these, or seen it happen first hand, may have a different perspective.