I think it helps to keep an open mind, I went to the UK the first time with the bf's perspective that his country has some of the best food in the world. And, I had some of the best meals of my life.
I still need to try that chip butty.... Maybe when I come over this summer. 
I think that's really true. If you just sit on the sidelines and judge, you'll never find out if some of that food is really good, just not what you're used to.
There's more than just peanut butter and jelly that would be weird to a British person, um green bean casserole (wtf? crispy salad onions and condensed soup with veg?!), chicken fried steak (I actually like these, but they creeped me out and sounded gross until I tried one), that weird yam thing with marshmallows on top, the number of sweet salads that get served with dinner (my inlaws make this grape salad thing which is blatantly desert and have it next to bbq
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), crag rangoons (deep fried cream cheese and crab meat?), slimy ocra, chilli and cheese on fries (what's up with that, is it necessary?), potato salad with eggs in it, getting a sandwich and it coming with a pickle on the side etc etc
Now I know that some of those foods are really great, but I wouldn't if I hadn't tried them. Different strokes for Different folks