Is a cinnamon bun a sandwich? Why not?

Definitely not a sandwich, because you can't pick it up without making a mess.

I get this question a lot: "Would you call this cinnamon bun a sandwich?"

Okay, you got me. I've never been asked it, but I've imagined such a scenario many, many times. 

The answer is no. It's not a sandwich. "Why not?" I've often imagined being asked in shocked awe. 

Easy: it's not easy to eat with your hands without excessive mess. 

Let's get theoretical. If it was easier to hand-hold it was would be considered an open-faced vanilla cream cheese frosting sandwich with a raspberry cinnamon bun frame. 

"But you have to bake it," someone might say. "Doesn't the fact that it's not in an edible state prior to baking disqualify it from sandwich-hood?" 

Iin this case the essence (the frosting) is added after the cinnamon bun is baked, so it's not unlike baking bread then adding a slice of ham, which is clearly a sandwich. 

But the above is not a sandwich. Too messy. See the Complete, Unambiguous Sandwich Definition for more.