This one is kind of long in the tooth, as emails that make the rounds go, but if you haven't seen it yet, it's good for a laugh.

Dear Hiring Manager,

Thank you for your letter concerning my application for employment. After careful consideration, I regret to inform you that I am unable to accept your refusal to offer me a position in your department.

This year I have been particularly fortunate in receiving an unusually large number of rejection letters. With such a varied and promising field of candidates, it is impossible for me to accept all refusals. Despite your company's outstanding qualifications and previous experience in rejecting applicants, I find that your rejection does not meet my needs at this time. Therefore, I will assume the position in your department next week. I look forward to seeing you then.

Best of luck in rejecting future applicants.