LOTS of people collect them , they are like POGS for adultsI would say a coffee cup... Wouldn't really be using an RO2 flask or shot glasses... I mean, who in the world would drink shots with RO2 shot glasses or would drink from an RO2 flask? Drinking your morning coffee from an RO2 mug however, that I can see happening, since there are so many corky coffee mugs in the world.