Actually let me rephrase that.
A vote for Bernie at this point, is a vote for Egotism. Why do I say this? This is a man who has SPECIFICALLY asked that you not do that, in order to make sure his candidate, Hillary Clinton is President.
If you vote for him now, over that request, it is really a vote for YOURSELF. You are voting for Bernie not because you want to make yourself feel good about something that isn't a real protest in any meaningful way. It is an expression of nothing. There will not be a magic fifth line on CNN's screen that says "and look at this, 20,000 votes for Bernie Sanders!".
It is to make yourself feel good in the very immediate sense - in the polling booth, and that's it. It's the very definition of a wasted vote, coming from the guy whose name you're writing in.