To PTB, is to "Pass the Buck". In other words, it's to delegate a task to another employee or department, when the said task has already been delegated to you, by another employee or department. It is meant to be used on a particular person when they are found to re-delegate tasks frequently.
Darren asked Dan to call everyone in the office to find out who was attending the lunch bbq, Dan PTB'd to Shaun, and Shaun had to call everyone.
When Bill delegated a task to his own supervisor, he was crowned the PTB king.