A top mug of the future is a person who is destined to be a complete idiot at some point later in time. This could take weeks, months or even years! You can usually tell when someone is a "top mug of the future" if they always do something annoying or stupid, but each time it gets worse.
1. You are just a 'top mug of the future'.
2. He is such a 'top mug of the future'
3. It's obvious he's destined to be the next 'top mug of the future'.