Honestly it depends on the sandwich and what I'm having with it on the side. For example, if it's just a turkey and cheese with mayo and maybe tomato and lettuce with I just eat it with usually the first bite being from a corner and alternating sandwich with chips. I also make some awesome grilled sandwiches with turkey, cheese, bacon, avocado, grilled onions, etc so it's kind of thick. These I have to cut in half diagonally from corner to corner to even think about eating it. It can get a little messy so I usually wrap a napkin to protect my shirt. Now the sides for this....I can go chips, but I often go with a cup of soup. This becomes a juggling act because I like eat sandwiches in the living room watching a game or something. Sometimes its a bite of sandwich then a spoonful or two of soup oooorrrrr I like to dip my sandwich in my soup. Mmmmmmmm. There's a lot of sandwich eating methods I suspect.
If we have sandwiches, sometimes I will roll it up and cram all of it into my mouth. Really gets Mrs. Bevojoe's dander up and I get the rather loud and stern lecture on proper etiquette, which I think is funny.
If I go with just meat cheese and mustard, I mashed the heck out of it. Why? I have no idea. Sandwich with all the works, I eat it like a gentleman.