How would you be able to tell the difference?
Well, as noted, the difference lies in the player's behavior. In essentially every case I've ever seen or heard of where someone uses this phrase, it's only given after the harmful act has been completed; it's used as an excuse or justification, a "well I had no
choice, I
had to do it, my character
made me" as though the character were totally external to their self/choices and they had zero responsibility; and, finally, it's given in response specifically to quite reasonable frustration, agreed upon by at least one (and usually most) players at the table. Usually, the "but it's what my character would do" is also only deployed after a
covert or
hidden action which did something harmful (and often VERY harmful) to one of the other PCs.
I have literally never seen a reasonable group of people, who talk to one another and respect one another's interests and preferences,
ever use this phrase in that way. It would instead be given
in advance, as a "man...I kinda think I need to do this dumb/dangerous/etc. thing...", which allows the other player to come to terms with it in advance rather than just having to like it or lump it. It would usually have at least a
brief window of opportunity to discuss it and maybe find an alternative. And, finally, it absolutely would not be covert--the action, if it did in fact get carried out, would be open knowledge to the group, not hidden away to only get discovered later.
Because no player has ever unjustifiably got aggravated with another’s play simply because they didn’t like the final outcome?
"Never", certainly not. But, in general, I find that that is usually pretty obvious at the table. That is, if most other players thought the situation was quite reasonable, and only one person got really bent out of shape, it's probably because the person who got bent out of shape had inappropriate expectations and is now butthurt to learn that those expectations have been dashed.
In either event, sitting down and having a genuine
conversation, rather than throwing up the fig-leaf excuse, is always the better option. Communication, even if imperfect, is
always better than making excuses after the fact. Checking in with others before you do things is almost always better than just doing things and demanding forgiveness or allowance afterward.
Because every player playing in good faith is a great communicator in the meta channels?
I don't understand what you mean by this.
I think you are demanding qualities here that aren’t specific to anyone playing a character meant to gel with the party, but might not in every conceivable circumstance in good faith.
...what qualities, now? I'm expecting that the player be sincere, that they think about the plausible consequences of their actions before they take those actions, and that they speak to other players if they think there might be issues resulting from the actions they feel they need to take. I don't see how any of that is in any way having unrealistic expectations. I see that as...expecting people to be communicative adults who treat their colleagues with respect. Is that really an unrealistic expectation at the table?
Sure. I’ll grant its rarity.
It certainly did not come across as indicating that it was a rarity. You made it sound like this was fairly common, as in, most groups will encounter it many times, such that it should be perfectly reasonable in nearly every case for a player to say "but it's what my
character would do!" and have that be an unassailable defense for crappy behavior.
Right. It’s why I said I think you went too far instead of I disagree.
And I don't think I've gone too far at all. I am quite confident that, almost all of the time, if a situation has arisen where:
(1) A player has chosen to do something
knowing that it would be harmful
(2) Another player has gotten upset because of that action
(3) At least one other player agrees that it's reasonable to be upset about that action
(4) The upset player has asked for a justification for this harmful action
(5) The player who took that action excuses this behavior with "but it's what my character would do!"
Then the player who gave that excuse is trying to justify jerkish behavior with something that
isn't a justification at all, trying to pretend that the character is external to them and "made" them do it when
they are completely responsible for 100% of the characteristics their character possesses.
I see nothing unfair, nor inappropriate, with saying that in the
vast, VAST majority of cases--certainly more than 99 out of 100--when a player is using this as an
ex post facto "explanation" for their behavior, it's because they're trying to get away with being a jerk.