First: OxfordDictionaries.com, which maintains the Oxford Corpus and attempts to track contemporary usage, is not the same thing as the Oxford English Dictionary, though the OED might well get around to some of these words in its own good time, particularly if they prove to be more than ephemeral.
Second (and more important): Remind the agitated party that the function of a dictionary is to record words and their meanings so that someone who comes across an unfamiliar term can discover its sense. If you didn't know that SMH means shake my head (I didn't), you would have been at a loss without a reference to turn to. Or do you keep a young person in your retinue to explain things to you?
Item: All retired English teachers have died. Not so. I know some.
Item: No one reads the paper any longer, so no one notices. Doubtful. Complaints from readers about many other matters continue to arrive.
Item: Singular they is increasingly acceptable and has become so familiar that people are used to it. What do you think is the likeliest possibility?