Re: stop me if you've heard this one....
Really did manage to do the "ask the guy in stores for a long weight" (for balancing a line printer's flywheel).
I (almost) felt sorry for the lad too. He fell for it hook, line, sinker, rod, fisherman chair, tackle box and bit of bank.
What made it even worse for him was that he was a ginger nut and blushed bright enough to be an aircraft warning light.
Happy days.
I also recall having to replace a dirty great ferroresonant power supply. Put the old one in the skip, went back in and realised I'd forgotten to dump the cardboard box. It was too good an opportunity to miss: I taped the empty box shut and made a spectacle of "staggering" back to stored, "straining" to lug the "heavy" box back. Went into stores, yelled to the store man "no good, all aortwd, don't need it, stick it back on the shelf" and tossed the box at him. Poor bloke nearly went through a wall trying to dodge it.
Happy days ^2