Back in St Louis, next door neighbor had just got a brand new Stingray (late 70's, possibly 78) from the factory -- got a good deal, as he used his dad's employee discount! -- and just HAD to change the oil. Prob didn't have 3k miles on it yet, but hey, new sports car, gotta do SOMETHING with it, right?
So Frank pulls it into the drive, gets the drip pan, the new oil cans and spout, new filter, toolbox, he's making quite a production of this. Drains the "old" oil, swaps the filter, drags out the drip pan and pours it into a jug for recycling (which is just getting started, so it's good that he didn't dump it in the gutter), starts pouring in the new oil.
I ask "Did you maybe forget something, Frank?" and he didn't forget anything, what do I know about it anyhow?, gets done. Closes everything up, gets ready to get in and start the car...and I wave him down and ask,
"Frank, did you put the plug back in the oil pan?" Yes, he did, don't bother him. "Maybe you better check again." Point to the stream of brand-new clean 30wt running down the drive and into the street....the plug was in the old oil, of course, in the jug.
He hated me after that, especially with him being in his late 20's and me being 16 and a girl! His dad said he felt embarrassed and his mom said he should be thankful I kept him from burning up the engine. He'd probably have preferred to burn it up. I never told anyone except Gramma and Grandpa, so any embarrassment he got was from HIM telling tales!
Never assume you did it right just because you're a guy :D