I wasn't the instigator but my reputation made me the prime suspect
This joke goes back to the early 1980s, and it wasn't I who was the instigator, but it turns out that I had done enough things like it that I was blamed for it. And I took that as the highest compliment.
I worked in a microcircuits design group. One co-worker we'll call Bob was a pretty theoretical guy--Ph.D, analyzed problems to a fault, took much longer to get to the bottom line than a practical person would by simply by taking the Thomas Edison approach.
The instigator--we'll call him Fred--was a very practical, hands-on guy, who would just go in and chug through a problem to get it done, then do the fine tuning later. Needless to say, there was friction.
We worked in a high noise environment. Our second-level manager happened to have a white noise generator at his desk to cover ambient noise and reduce stress, and Bob asked to borrow it one day to see if he wanted to get his own.
Manager said he would drop it at his desk at the end of the day, and Bob should try it all day tomorrow, as that's the only way to really give it a good assessment.
The manager dropped off unit, and Bob left for the evening. Fred sprang into action. He disassembled the white noise unit, happily noted that the 120 V power into the box was switched through a DPDT switch, and found a battery and a lift truck backup alarm in the engineering stockroom--which he proceeded to wire across the unused half of the DPDT on/off switch.
It all squeezed inside the box, so he taped it down tight, reassembled the unit, and replaced it at Bob's desk.
Next morning, Bob came in, plugged it in, hit the switch, and of course the backup alarm blasted away and drowned out the white noise, which was still working.
Bob jumped up, amazed.
Quickly his curiosity led him to come up all sorts of theories about what happened--seed for shift register got the bits synchronized in a long 1111...0000 combination, one in a million chance that this could happen, etc. blah blah blah.
He went to manager to express amazement and explain all of this. Somewhere in the process, though, the unit got unplugged and used as exhibit "A" to explain his long-winded theories about what happened, without Bob noticing that the power cord was dangling down on the floor by his feet while the alarm was still blasting away--at least until manager noticed, grabbed the plug end of the cord, and held it directly in front of Bob's face.
After staring at it a few seconds, the idea that it was a joke finally sunk in. They took it apart, discovered the modification, and went looking for the instigator--which they thought was me.
My protestations of innocence only reinforced in their minds that I had done it.
Fred only admitted to me much, much later that it had been him.