Write a card like this and send it to the Democratic National Committee, and you can claim jackass status for life.
First of all, these people were not really Democrats. They were independents or people that do not usually vote. How do we know this? Many of them never bothered to vote! If they had actually voted for Bernie Sanders, he probably would have won.
Second, the DNC does not care about your Goodbye Cruel World statements. They have hundreds of other races that have to be won against the Republican Party. If you don't care about working people, women's reproductive rights, veterans, the disabled, LGBTs, and minorities, you weren't going to vote for the Democratic candidate in the first place. Everyone who is an adult is already on board.
Third, this is not how elections and democracy actually works. In our system, you choose one of the two main parties and vote accordingly. Any other use of your vote is a waste because this is the system we use--a two party representative democracy gives you a chance to participate, and if you throw that chance away, that's on you.
We have to stop worrying about these people and their feelings. If they're not on board, they're never going to support Hillary or do the right thing. They will act like upset customers and take their votes elsewhere. Let them. They are irrelevant and they know it.