Either humour or an insult - depending on your relationship w. the departed! Give as "Going-Away Gift". It's BLACK when they get it. When they get to actually USING it (with a hot beverage), the message becomes visible as the mug lightens in colour. They'll either laugh hysterically at the belated jab -- or realize that the going away party was merely a formality! A great gift for either Hawkeye Pierce -OR- Frank Burns types!