I grew up drinking milkshakes, but I didn't know that sharing one is a thing in America! So, add another two billion people to that number (highly scientific estimate).
The whole soda fountain phenomenon was before our time, so I'm not sure that milkshakes were available at most soda fountains, but it's easy to imagine the tableau relocated to the ice cream shop. The "milkshake icon" seems more evocative than the "soda icon".
