This wasn't me but an old co-worker of mine. When I was just out of high school I got a job installing radios and alarms into cars.

There were about 5–6 guys in total working in the install bay to where the sales guys (from the air conditioned sales floor inside the building) would bring us the products to install, along with the cars keys after having sold something.

It was no secret that John, a sales guy in the store had a c@nt girlfriend and he was always in a bad mood and taking antidepressants due to the way she treated him.

One day John was really upset and told us his girlfriend broke up with him because he didn't have a "real" job and didn't earn enough to support her I.e. he wasn't a "real man".. I guess the breakup was pretty nasty and just to prove a point, about 3 weeks later she made sure he was working and drove to the store in a new Lexus which her new "rich" boyfriend bought for her. They both went in and asked for "John", her ex, to sell them the most expensive amplifier, for which the new guy paid in cash.

The girl had an enormous, smug smirk on her face the whole time and then said loud enough for everyone to hear "let's go eat a nice lunch while the help make my new car loud"… and then they left for about 2 hours.

John had told them that the amp must go under the passenger seat due to the car being a convertible and not much space in the back. They agreed.

We were pretty amazed at the Pokerface John kept the whole time but then he came back to the install bay with the amp (known amongst us it tends to really heat up and it was summertime).. he puts it on our bench and says "you guys mind if I install this myself?"
"Sure" we all said while grinning.
There was an apartment complex next to the store where all the people with dogs would take them and have them poop/pee on the grassy patch between parking spots behind the store. Of course, not everyone picked up their dog's poo.
John went out there, picked a nice, fresh but smaller turd from the grass, came back.

He took the seat out, wired everything in to the amp's place but before mounting the amplifier, he carefully placed the dog turd in the middle of the carpet and then carefully placed the amp on top, then screwed it down…

I didn't find out what happened afterwards, only saw her come back, grab the keys and drive away with her new man, blasting the radio. I'm sure the smell caught up eventually every time the amp would heat up..