Dear IRS, I am writing to you to cancel my subscription. Please remove my name from your mailing list.

The line is a joke built on treating an unavoidable civic obligation—paying taxes—as if it were an optional commercial service. By addressing the IRS like a magazine or marketing list (“cancel my subscription,” “remove my name from your mailing list”), the speaker highlights the frustration many people feel toward taxation and bureaucratic correspondence, and the fantasy that one could simply opt out. The humor comes from the mismatch between consumer choice and government authority, and from the polite, formal tone applied to an impossible request.