My pop gave me a buick skylark about 8 years ago. Anytime I get a vehicle the first thing I do is give it a tuneup and oil change regardless of what the PO tells me. My pop told me he was keeping up with the oil changes on the vehicle. I drain the oil and it's sludge. I go to take of the filter and it collapses under te filter wrench it's so tight. I wind up punching through it with a screwdriver and turning it that way. During a phone call that left me speechless my pop told me in the last 3 years he never 'actually' changed the oil or filter. It used a quart every 2 weeks so it got 4 quarts of oil every 2 months which was 'like' an oil change
Then there is my father in law. He is a nut about oil, but he's cheap. All our work trucks get dollar general oil and $1.50 fram filters every 4 months or so.
Then there was the time he topped off my flatbed. I had it parked ready for the next day and before I went out he took the liberty of checking my oil (which I did the night before). SO I start the truck and let it warm up and smoke starts pouring out the exhaust and from under the hood. I pop the hood and oil is EVERYWHERE. It's dripping from the bottom of the hood and coating every surface as well as burning off the manifold. I open the air cleaner and the filter is saturated and oil is puddled in the air cleaner. He sees the smoke and comes out to find out what the problem is. I ask him if he messed with my truck that morning. He says yes and bitches at me for running it so low on oil, he had to put in 5 quarts that morning to get it up on the dipstick. I then had to inform him that a 351 only holds 5 quarts including the filter and I had topped it off that night. I had parked the truck in front of our building the previous night which is a hill. So my truck had 10 quarts of oil in it and blew it out of every orifice it had (and I believe it ruined the rear main seal that eventually killed the motor).