Speaking of sushi - people that pick the top of nigiri or generally just dissect it in some way is a MASSIVE crime.
Sushi is an absolute culinary ART, and as such it should be treated with the utmost respect. The ingredients are chosen, prepared and presented in such a way that you should view it as the perfect representation of what it should be. So if you peel that ebi off the top or rip the nori off, you're effectively telling the chef he sucks. What's the point?
Also, if you're going to scarf it down like you're eating McDonalds fries, that's equally pointless. Nigiri should be eaten rice side up, topping side down, so the fish/meat/vegetable hits the tongue first, dissolves and develops, then the subtler rice and then the bitter vinegar join the tastebuds into a delicious symphony of flavour. Otherwise you're getting a gobful of rice and chomp it up, and "Oh, what kind was that?"
"oh, some kinda fish".
"oh, cool."