"Not my president" has been the rallying cry of protests against the election of Donald Trump. Did any of the protest leaders think this through?
If Trump is not their president (elect), then where does that leave them? Trump IS the president-elect of the United States of America. Like it or not, that is how the election came out. I've voted in every presidential election since 1972, and many times my vote was wasted on a runner-up for the office. Still, I recognized that in a democracy, as in most of life, you don't "always get what you want" (thank you, Rolling Stones), and I grudgingly accepted the fact that a majority of voters (or electors) selected the person I didn't want.
When someone is elected president of the United States, he or she is the president of all the people — those who voted for him/her, those who cannot stand him/her, those who failed to cast a ballot, those who are giddy at the outcome and those who are angry about the outcome. None of these can rightfully claim "not my president."
Unless, of course they want to really do something about it, such as forsaking their American citizenship, moving to another country — presumably with a leader more to their liking — or starting an insurrection. They should be warned that some secessionist in South Carolina tried that option 155 years ago. They declared that Abraham Lincoln would never be their president. It didn't go well for them.
You can spend the next four years opposing Donald Trump and all that he does, but until you give up your citizenship or a new president is elected, you cannot say he is "not my president."