A worthwhile discipline: when giving feedback, separate "not for me" from "not for anyone."
If someone brings you a business plan for a power plant that will use perpetual motion as a power supply, it's fair to say, "this will never work, it's impossible."
If someone brings you a business plan for a chain of hot dog sushi restaurants, it's fair to say, "this is disgusting, I will never go here," but not helpful to assume that it won't work anywhere under any circumstances.
You can say you don't like a book or a movie or a political candidate, but without more data, it's impossible to say that it won't succeed, get great reviews or even get elected.
Brilliant editors and venture capitalists have the ability to get excited about a project that perhaps doesn't match their taste–or to criticize it based on experience, not selfishness. This is a really valuable skill, as it requires empathy, experience and judgment, not just the knee-jerk ability to pontificate.