That's a really strange interaction. Maybe it would have been better to directly ask the homeless guy to chime in on the diabetes thing (and maybe offer a different beverage if he actually had diabetes?), otherwise I'm at a loss as to how I might have handled the situation differently.

At the same time, if the guy actually had diabetes but still wanted the coke, it seems like it would be weirdly patronizing to insist on a healthier alternative for the guy who still has to live on the goddamn streets. Like "Oh, be devoid of basic necessities, but we can't let you have a soda because it would be bad for your health." I don't know.