A printed mug works as a gift because he uses it regularly and sees the design every morning. The humour should match his actual sense of humour rather than generic dad jokes. A quality mug has a substantial feel and proper printing that does not fade after a few washes. Ceramic feels better than cheap plastic. The design should be something he does not mind being visible in a work mug situation. Avoid anything too crude or inside jokes that no longer land. These are the mugs that raise a smile every morning without being so specific that they become embarrassing to use in public rather than sitting in the back of the cupboard because the joke landed wrong.