OK.
I went to collect a client's pension. A snooty Post Office clerk informed me that as a new book had been issued the old one must be destroyed
in case of fraud, looking pointedly at ME, as if I was a natural pension-thief. Highly offensive and unnecessary.
She then proceeded to tear in half THE NEW BOOK.
I said 'Haha, you're ripping up the wrong book!' and her snobby face filled with horror as she realised I was right, too late to stop her hands from moving.
I was immediately hysterical with laughter, pointing and roaring and wiping away tears of hilarity.
She said 'It's not funny!' and I said 'Oh yes it is!' and laughed harder.
I then demanded that she a. inform her supervisor of her mistake b. write a letter of explanation to the client c. also ring the client immediately to inform her of it and d. repair the book as I would need to produce it to prove I hadn't stolen it.
The client was a hateful, suspicious old bag who deeply resented having to hand over her pension book so I wasn't taking any chances.
The next half hour or so of humiliation for the clerk was deeply satisfying to me. She taped all the torn pages together and made the phone call in front of me, and the supervisor and I helped her draft the letter.
I laughed the whole time and the memory amused me for many years afterwards. Still makes me giggle.