Pardon the punctuation errors and misspellings in the above post (“SQUAK?!”). It’s too early in the morning.
For what it is worth, in my humble opinion, a lot of times the squawking after some “unwritten rule” is broken comes from those who are unhappy the particular feat in question didn’t get accomplished, and are still being emotional rather than rational about that fact. Brenly always was emotional (as Giants and Dodgers fans will easily recall). With reflection, most likely he would WANT the hitter to have swung, but admit grudgingly that bunting wasn’t completely classless (as, say, trying to behead someone on the opposition just because they hit a home run, or getting elated over a home run that makes the game 15-0).
It is this same tendency to allow emotion to cloud action that causes players, managers and fans to be upset with decisions made by referees and umpires, even when the evidence is pretty strongly in favor of the decision made. As a soccer referee, I get this all the time; I realize that most of it is the emotion of the person who wants things to go well. NOT that it hasn’t resulted in a yellow card or two… 
Unwritten rules are worth the paper they are written on. It was a brilliant play by Ben Davis to get on base against a dominating pitcher.
Well, I briefly hoped that there might be a standard, accepted answer to this question, but if there is, it doesn’t look like we’re going to get it. Off to IMHO.