This has to be one of the best threads I've seen in a long time (also making me hungry too)
Tacos could be sandwiches, but sandwiches are usually between two slices of bread, while tacos have their contents in a taco shell. Also, just having it as meat, onion, lettuce, and mayo is a bit generalizing. I mainly have my taco as just meat and cheese, and my sandwiches usually have lemon curd spread
Oh and what about the Swaco and the Tanwich?