What defines a sandwich? Is a hot dog a sandwich? A taco? Bao? Where do you draw the line?

The UK office worker seemingly lives off pre-packaged sandwiches and the United States has eateries devoted to freshly prepared hot sandwiches so why does Australia seem to cling to its toasties. Thankfully, the tide is changing. 

More and more sandwich joints are opening around town offering freshly made hot or cold sandwiches that will leave one very satisfied, if not in need of several napkins to wipe their face clean. 
Body positioning is important to spill it all down the front of you, ergo the Philly stance.

Classics are classic for good reason. 
*pan bagnat – make ahead, oil soaks into bread a little so doesn’t dry out (salade niçoise but in sandwich form – olive, egg, tuna etc)
*banh mi – balance of flavours and texture, chilli punch, fresh salad, not heavy but satisfying
*finger sandwiches – look fancy with the extra effort trimming edges, not over-filled so easy/clean to eat while standing with a glass of champagne in one hand
*BLT – balance salt crispy bacon, creamy mayo, sweet acidic tomato, lettuce vegetal freshness
*NYC bagel – cured salmon, cream cheese schmear = cultural ties but also delicious. Richness of filling vs chewy ubiquitous bagel
*chip butty – hot chips in buttered white roll – carb on carb delight

Do you have a favourite sandwich or, conversely, something that should never be seen between two pieces of bread? From my childhood days, I recall my mother enjoying an apricot jam and cheddar cheese sandwich. No judgement here.