I always arrive late for work, but... round clock

I like this math! If early and late cancel each other out like adding negatives and positives then "I always arrive late for work, but I make up for it by leaving early" works. Well, don't tell your boss. And, if your boss gives you this mug you might want to start coming in a little earlier and leaving a little later. It might be a hint that something is wrong with your work ethic. But, for most people, this is just a little fun with some flawed logic. (and funny logic at that.) So, be a little sarcastic and maybe share a little tongue-in-cheek humour.