when does a sandwich stop being a sandwich?

I was eating a sandwich in public today. The public part is important to know because if I was home alone and eating this sandwich I would not care so much about manners.
Facts of the case
I stopped for lunch and ordered a chicken patty sandwich. The bun was smaller than the chicken patty and when I finished eating the part with bread I was left with more chicken so I picked it up with my fingers and ate it without using a fork. Then I had this horrible feeling that I had committed an aggregious offense. I looked around to see if anyone had seen my error and then I really wanted to know - when does a sandwich stop being a sandwich?


Issue: eating in public with my fingers
Rule: it is not polite to eat with ones fingers in public unless it is finger food- or wrapped in something or nestled between two pieces of bread, the latter we call a sandwich

hors d'eourves are eaten with fingers, amuse bouche with fingers, tacos are eaten with fingers- but when a taco is baked and covered with sauce- it is now eaten with a fork. (but I digress- probably why I am not in law school anymore....)

we need more references:
a potato
chopped, boiled and mixed with dressing- fork.
baked- cut open, filled with butter, and other stuff - fork
sliced, breaded, fried- fingers
sliced, breaded, fried, smothered in chili and cheese - fork

so the answer could lie with the messyness of the food itself.

apple
washed eaten raw - fingers
cooked in any way, apple sauce, apple pie,- fork
one exception is when baked into a small pastry (yummm krispy kreme)
the other exception is when made into a condiment such as apple butter- spread it on a piece of bread and you have a sandwich.... which leads back to the original issue....

sandwich
cold or hot bread- two peices filled with "stuff" - fingers
one slice of bread topped with "stuff" - fork
exception- grilled cheese fits the "topped" rule and not the two pieces rule...
but the open faced turkey sandwich must be eaten with a fork.

more sandwich thoughts...
there is a hot grill that clamps bread at the edges- so just about anything could be put between two pieces of bread and be called a sandwich....
so, macaroni and cheese could be clamped on the edges with one of these gadgets (what I want for Chanukah, btw) and be considered a sandwich.
if you pick it up with your fingers and bite into it and some of the mac n cheese falls onto your plate, I would say you have to eat that with a fork or a spoon.
but why?
back to the messy factor.
If we place a slice of pastrami on rye with some spicy mustard and some of the pastrami falls off the sandwich and on to the plate- but you still have bread left in your hand--- can we just pick the fallen up and place directly into our mouths or must we re-attach the meat back into the bread- and then place into our mouths....

this is different from the original issue-- because in the original issue- I ran out of bread and still had chicken left over, also there was only one large bite left over...no more sandwich- no more socially acceptable finger food.

so new question, when does a sandwich lose it's sandwichyness?

sushi is eaten with fingers in Japan, but not in the US. so could my answer lie culturally?
what do we eat with our fingers that other cultures eat with forks...
In Paris there are patisseries on the corners of the streets where beautiful thin women purchase small pies and scarf them down while walking down the street....
In the US- we sit down and eat pie with a fork and plate.
Parisians are thinner than Americans, maybe we should eat pie while walking and not sitting down- maybe that would help the obesity issues in this country...
maybe if we ate all of our foods with our fingers we would be thinner-

think about it-
we eat messy foods with forks- what makes a food messy? cheese, gravy, sauce,
hmmmm.

gotta go play poker...