Right, a lot of people I know either don't like fish or they don't like mayonnaise.
I can understand the second one. Maybe you like Cool Whip. Maybe you'd like homemade mayo (which is awesome and really easy, by the way). Either way, I get it.
But fish? To simply say "I don't like fish" is like saying "I don't like vegetables" when there's such a wide variety of tastes, textures, colors, and styles of preparing them. This is one of those things that, try as I might, my brain is never actually able to comprehend.