Most people think of ceramic coffee cups, but just as usable are glass coffee cups. The usefulness is not too much different. Ceramic and glass are both chemically inert and both need handles in order to avoid touching a surface heated by coffee. The major advantage of glass is that it contains no additional substances and might be preferable for a person concerned with leaching from hot ceramics.
Glass is completely pure and also looks attractive as a clear container. The user can clearly see the coffee level, and so can other people in the room. It is a more direct way of admitting that a person loves coffee, and it is a curious difference from a regular mug. It does that same job, and the coffee tastes just as good. The coffee might taste better if using glass provides peace of mind.