They do have a sense of humour sometimes
Year before last I found a bug in the property section of the online form. Called up. "Let me try it" she said. Pause. Oh dear, you're right."Good" I said "is there a bug report bounty?" Cue helpless giggling from tax lady.
On a more serious note, I have by my desk the case files for a friend, recently deceased, who was the only private person ever to win the right to take HMRC to the European Court of Human Rights.You *can* beat the man.