Why is Dr. McCoy so irascible; i.e., who pissed in his Cheerios™?
(By the way, irascible my new favorite word that I never had occasion to use before...if Karl Urban uses it all the time, it's good enough for me)
Although actually, I think (and hope) that when we first come upon young McCoy he will already be the crotchety and disagreeable grump the we all have come to love.
OK this is a great one! Maybe he had a tragedy in his life that we will witness in the new movie that caused his irascibility. Also may be the reason he fell so hard for Natira?
Well, that's not something which has never been answered... we know the answer to that and have known it for over 40 years... with an addendum that came something like 20 years ago.
McCoy was always a smart-ass. His basic personality wasn't formed by any major event as an adult... but there are events which formed his attitudes.
1) He was married (to a woman whose name was never mentioned) and went through a really nasty, ugly divorce. He had a daughter through that marriage, named Joanna, and he ended up estranged from both the ex-wife and the daughter. Since we never hear about Joanna again in-canon, it's not unreasonable to assume that the estrangement is a permanent one, though that's speculative.
2) We know (from ST-V) that McCoy was his father's private physician (a generally bad idea!) when he was dying, and that he euthanized his father (at his request) to end his pain... and that there was a cure for the disease which was killing his father found soon thereafter. While it might seem reasonable to assume that this happened when McCoy was older (based upon the presentation in the film) it's worth noting that what you were seeing was through his memory... this might've happened when McCoy was quite young... and it's clear that it happened when he was not in active Starfleet service.
3) This is not hard-and-fast, but it's always been evident to me that McCoy, unlike most of the other folks we see in trek, was not a "career regular Starfleet man." Rather, he was more in the vein of Hawkeye Pierce or the others from MASH. He got his education and training as a civilian, but because Starfleet needed special-skills folks like him, they brought him in (probably at an O-3 rank similar to Hawkeye... in Starfleet, that would be a Lieutenant... by the time of TOS he was a Lieutenant Commander, which would imply that he had served for around six to eight years in Starfleet at that time, max.
4) It's established that McCoy is older than Kirk by a number of years (McCoy and Scotty were the two oldest "key players" on the ship as I recall... disregarding any of the age issues which may or may not apply to Spock and "vulcan years versus earth years")
So... why is McCoy the way he is? Part of it is inherent... and part if it is learned, through pain and suffering... and his desire to compensate.
I've always wondered if, perhaps, it was an affair with the REAL "Nancy" which resulted in McCoy's divorce... or perhaps he was just a player in general (based upon Dax's comments in "Trials and Tribble-ations." In any case, by the time of TOS, we see very little evidence of him as a "player" in any sense, other than on the "shore leave" planet (which is, after all, entirely FANTASY and thus entirely "safe" for someone who's been stung by his own tendency to play around too much in the past!)
I'm still very hopeful that the McCoy we see in this film won't be in Starfleet (yet), and what we'll see is the event(s) which convince him that this is how to find meaning in his life.
As for why he fell so hard for Natira... that's obvious (and it's really unfair to her!). He had just found out that he was going to die of a terminal illness himself. (Relate that to the death of his father!) So he was desperately seeking a legacy... this is a very common reaction to that sort of situation. It's VERY interesting to note that when his illness was miraculously cured (by HER, essentially, no less!), he didn't hesitate to run off without her. Basically, he was USING HER for emotional support, and when he didn't need her support anymore... off he went! (At least Roddenberry's novelization for TMP implied he went back to visit her between TOS and TMP.)
