Telling it like it is

I just can't look someone in the eye and tell them I don't like their food/clothes/children/etc., even when I know that such an admission is needed unless I plan on partaking/wearing/dancing attendance on future iterations of the experience. Really, I'd choose to grit my teeth and bear it, even if I didn't like it/enjoy myself. Still, I understand that there are people out there who would be genuinely horrified to find out that we were all perpetuating an unnecessary lie. So how do you politely, earnestly, and gently tell it like it is, without hurting anybody's feelings?