In the CHE today "Female Science Professor" writes, "If you don't like another professor, don't take your dislike out on their students and postdocs." I am always irritated by that use of "their"--the plural pronoun with a singular antecedent, utterly illogical, calling attention to its lack of gender bias.
Mine doesn't seem to be the majority view. Those whose opinions I respect remind me that the usage goes back at least to Shakespeare,"God send every one their heart's desire!" Thackery writes, "A person can't help their birth." And "in lowliness of mind let each esteem other better than themselves," says the King James Committee.
I don't care. I find the construction, as currently used, smugly self satisfied in its correctness (and, yes, I'm probably projecting here), but each person must please themselves.