I've received calls with WA DC in the caller I.D. Always a foreign accented voice telling me that I owed such and such and that I would be prosecuted f I didn't agree to pay by credit card, no less, immediately.

Me, because I AM a glib smart-ass, "hey asshole, the IRS doesn't do outbound calls. Period.

I have your phone number in my caller ID, and shortly the FTC, the FBI and the IRS will have your number too."

They usually beat me to the 'hang-up'.