You, on the other hand, are flat out. Of course you'd like to take a moment to sit back and relax, but the work just needs to get done... and so, you pick up the slack.
This isn't at all an uncommon occurrence. In fact, the irritating work habits of your free-loading work mate actually has a name: social loafing.
Watch: Why I last cried at work. Post continues after video.
Put simply, 'social loafing' is a term used to describe people putting in (much less) effort when they're in a group situation.
It's something a lot of us probably first experienced in school, after being assigned to a group project with a few classmates (there was always that one kid who did nothing right?!).
While one person in the group coasted along, dodging their portion of the assignment, others (you?!) drowned in the workload of several people. Because ultimately, the assignment was judged as a whole, and everyone would receive the same mark – with no extra points given to those who worked harder (and no ramifications for those who sat back and enjoyed the free ride).
It's annoying enough in the classroom, but this kind of behaviour at work can be extremely problematic – and many of us have experienced it.