When I was young, I worked at a pool. All of us had to work the snack bar at one time or another. I use to give kids carbonated water straight and tell them that Coke was trying out a new drink and I was to let them have it for free. I'd fill my glass with regular water and show them how I was drinking it.

"This stuff is great, what do you think? (Sip)."

"(Gag). Yeah, it's pretty good. Thanks mister."

Then they would walk off and never come back to the Snack Bar again.