A customer once accused me of rusting his headset bearing in the one single day the bike was with us for a service.
Another customer refused to learn how to shift gears and preferred to have his bike eat derailleurs and then come in and shout and scream about the rubbish derailers we keep on fitting to his bike.
Then there's the customer who accused me of using the wrong type of oil in his suspension fork the previous time it was serviced and that is why the fork now, 200 hours overdue for a service, has stanchion damage. The thick mud under the seal's lip had nothing to do with the damage, it was the type of oil.
Then there's the one who broke her bicycle computer but managed to glue it back on with sparrow spit or something and the minute I touched it, it broke off again. I was accused of breaking it in front of her eyes by the way I was touching it. That warranted, she said, a brand new model, preferably wireless, with cadence and wi-fi and all wheel drive and aircon, to compensate for her stress.
I usually ask if they'd like me to apply Vaseline before I shove their precious bike into a dark place. Except the guy with the rusty headset bearing. He was much bigger than me. I offered him a cup of tea I made from water I scooped out of a porcelain "well" in the gents...I wish. I always think of these things far too late.