PhD - permanent head damage

Have you ever wondered what "PhD" actually stands for? Besides the far too obvious definitions I dug out some other convenient possibilities:

• Permanent head damage
• Pizza Hut Delivery
• Piled Higher and Deeper
• Productive Happy Devil
• Public Hated Degree
• Patiently Hoping for a Degree (me favourite)
• Progressively Headed Downhill
• Pulsating Heaving Disaster
• Pretty Homely Dork
• Pathetic Homeless Dreamer
• Pour Her a Drink