Uncle Pug:
1) Do you offer to dive with the newly certified and obviously nervous fidgety guy who already has his reg in his mouth while sitting there on the boat? Remember... you are a noble soul... you were once a tadpole.
As it happens nobility doesn't come into play... the DM *assigns* you to the fidget. It is as you surmised... he is not only a tadpole but a shop vac. He sucks his air down in what must be record time. You've barely gotten to the bomies and the soft corals beckon... but your *buddy* is showing the DM his gauge and you know what that means.
To be honest, I would not offer. If I dropped a large amount of cash and flew a long ways to dive, I want to dive. If I did not have a choice in the matter, as per your scenario, I would talk to said diver before the dive about how
they would be getting back to the surface once he ran down his or her air (yes, I said 'they'), and once they were back on the boat I would continue my dive.
Uncle Pug:
2) Do you inwardly wish that the DM would just take *your buddy* and allow you to continue your dive since you still have 2/3 of your air left?
No, not really. I would ensure that he or she reached the boat safely, then I would continue my dive (I did this exact thing in Provo last week diving with my father-in-law). If this is not an option (continuing my dive), I have to admit I might be cheezed.
Uncle Pug:
3) How do you feel when the DM gives you the <pairupwithyourbuddyandascend> signal?
Again, if I had no option but to ascend and exit the water with the other diver I would be fairly annoyed.
Uncle Pug:
4) How do you feel back on the boat as you sit out what would have been 45 minutes of your dive while the *shop vac* exults to the skipper how great the dive was completely ignoring you?
I would talk to the DM about an alternate plan for the next dive(s), one involving me not getting out of the water but only escorting the other diver to the boat platform. If this was not an option, I must admit I would be quite annoyed and ask to dive with another person.
I just got back last night from the Turks & Caicos, and we had to deal with this very issue. My father-in-law could suck start a Harley, so what we worked out was the four of us would start the dive together. Once he got to a half-tank we would start for the anchor line. He would ascend the anchor line while the three of us would continue our dives for another 20 minutes or so under the boat.
Jimmie