Mug and coaster in one. I don't know; I usually don't use a coaster anyway. Precarious? Prone to dripping water down the coaster when it's used, because the coaster surface is not absorbent?
Previously:
Beer mug transporting trick - GIF
Bottoms Up reverse draft beer cup filling system - GIF and video
Flip out automotive cupholders - GIFs
Plastic cup manufacturing GIF
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