When "friends" split a check, advice needed on getting them to fair share

[Dennis S]

Announce assertively, "I had a Diet Coke. Here's my money." Slide the money toward the center of the table and then sort of become aloof to the rest of the prceedings. How can they quibble with that? In addition, everyone else's bill will rise and maybe some of them will turn on the worst offender and change the plan.