Voting Green, Libertarian, or writing in Bernie in November won't be "sticking it to the establishment". It won't "piss off the elites", they'll be fine. What you ARE doing (especially in key battleground states) is hurting us. You know, your fellow humans. I know that every year it's "important", but our choice is especially stark this November, because Trump is DANGEROUS, not just misguided or wrong.
I hope you're not thinking a vote for a 3rd party will cause that person to be elected, because no third party has that much support, period, no matter what you wish it to be. So your vote is a "protest" vote. I get it, I really do, I'm not 100% for Hillary either, and sometimes Dems piss me off. I disagree with her (and their) Wall Street ties and semi-neocon approach to the world. But I only have two actual viable choices in front of me: Trump or Hillary.
But your protest vote will have the effect of (possibly) electing Trump. He is unstable, anti-science, incompetent, racist, anti-Muslim, and pseudo fascist. He will choose SCOTUS justices that will negatively define us for a generation. He will start wars, piss off our allies (hello yesterday's NATO bombshell?), and more than probably, tank our economy.
I remember having this same discussion in 2000 with Bush v Gore and Nader/SCOTUS being the spoilers for Bush. How did that turn out? The most successful terrorist attack on our soil in generations, illegal wars, warrantless wiretapping, a banking system & economy brought to the brink of collapse, and a massive redistribution of wealth. Some of this has thankfully been rolled back by Pres Obama. Some more will be rolled backy by Hillary, but Trump will triple-quadruple down on this, and add some SCOTUS nominees that will pledge to roll back LGBT rights (starting with, but not limited to marriage rights!) & affirmative action, support Citizens United, and put at risk a woman's right to choose.
When you vote, have some empathy towards your fellow citizens. Or at the very least look to your own interests, because Trump WILL NOT.