Find a new job first, then quit.

I am not part of nor associated to YC but I wouldn't worry about this, good YC founders know there are bad YC founders (same for techstars etc) -- FWIW I have worked with YC founders. Being in the "club" doesn't mean you are necessarily "good", just means you passed a bar that YC thought they could make money on that served a need. That isn't a dig at YC or any other accelerator, it is just how it works.

If they speak badly of you it is more about them than you, and it might work once but if they going there it will backfire on them. Plus there are 100's of other startups outside of the YC ecosystem, look at those if you are worried.