I know, with all this experience and time served; there are a lot of great stories our contributors have to offer.
I once worked for a dealer in a bigger city (with an interesting customer base) and overheard a counter guy's interaction with a customer:
Customer: (part in-hand) I need a cruise control servo for my '89 Celebrity
Counterman: No problem! I have one and it will be $XX.XX plus the core charge. I see you've brought the core with you.... (core is returned to GM and so on)
Two weeks later, customer comes back, pleading with this counterman to have his old servo back because the new one "didn't fix his problem". After a while of explaining reasons why he could not have it back, regardless of the fact it was no longer in the building, the counterman began to get a little smirk on his face.
He told the customer "Can you spell DOG as in dog house?" The customer replied "D-O-G". The counterman asked "Can you spell CAT as in cat scratch?" The customer replied "C-A-T". The counterman said "Can you spell F@#K as in cruise control servo?" The customer was perplexed but replied "There is no F@#K in cruise control servo."
Counterman: "THAT'S WHAT I'VE BEEN TRYING TO TELL YOU!!! THERE IS NO F@#KING CRUISE CONTROL SERVO!"
That was 33 years ago. There are many more, but that is my all-time favorite.