After all these years, I finally suggest that we use a token system to keep track of who's turn it is to pay. If you have the token, hand it over and you get a free lunch! I'm not going to mint a gold coin, so I folded up a glorious piece of paper and drew this:
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This is the same guy who collected multiple lunches and asked if he owed me...
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He tried to pay me in Japanese Yen
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He does not own a cell phone. If we get split up, I can't track him down.