I did have this happen to me... I had a finished top with a bottom corner block upside down. I didn't think it bothered me that it was pointed out. This was someone I didn't know. But it made feel -- well -- less accepted by this person. I know that none of that is logical and I intellectually accept that, but my gut wouldn't let it go. So I wouldn't point out a mistake except to someone I know pretty well or if I was asked to evaluate the work.