Two proteins that I have never enjoyed are liver and octopus/squid.
I try a bit of someones probably once a year (maybe a bit less) - but have found it consistantly horrible.
I'll keep trying every once in a while though - maybe someone prepares it in a a way that I like.
The list of foods that I'm not interested in, or don't add anything for me is quite a bit longer, but inclused most mushrooms, artichokes, bitter leafy greens, many tropical fruits...
If you're up for exploring octopus/squid options yourself, there are some great treatments being presented in in the current Cook-Off 62: Squid, Calamari and Octopus.