Dear XXXXXXXXXX
After an appropriate period of deliberation, I have come to the decision to turn down your offer. Please know that I still maintain a high level of respect for you as a professor, and I thank you sincerely for the generous offer.
As such, I have decided to become a professional pirate. It has always been a dream of mine to live the life of a swashbuckling corsair, beholden to none and master of all I survey. Once my crew of unabashed rogues is assembled, we shall take to the capacious expanse of the high seas to pursue fortune, fame, and hair-raising adventure.
Our path may not be filled with the porcine comforts and technological marvels that (your university) provides, but we shall nonetheless move forward to carve a name for ourselves in the annals of bold insurgency and death-defying derring-do. Once I have a keen blade at my hip and the Jolly Roger is flapping high above me, I believe I will find my true calling.
Please note that I am currently accepting applications for First Officer, if you are at all interested in applying. I will provide a full medical and dental plan, which will offer immediate coverage of all maladies other than scurvy and the occasional bout of rickets.
Sincerely,
(your name)