Strange Human Behavior: Lunchtime

I've seen this time and time again, at Subway, at Hardees, at the Market Building, anywhere a quick lunch can be had: guys who are obviously together, arrived together in the same truck, going back to the same job site afterwards, who eat lunch together but at separate tables right near each other.

Usually, both are facing the same direction, and one guy converses over the other guy's shoulder. Sometimes they face in perpendicular directions. Today, I even witnessed a musical chairs kind of dynamic, where one guy initially sat down facing his companion's back, but then turned a 180 and sat back to back with him. Yet they continued on the conversation!

What this leads to, generally, is a loud shouting match so each can hear the other. What is going on here? Why not just share a table and save the other one for someone else? Sometimes it's because one or both have two or three sandwiches all laid out, but still, I don't get it. What are they afraid they might want to hold hands?