My late cat, Booger was an interesting character. He was 18 pounds of fluffy orange Maine Coon. Some of my favorite quirks of his...
He was very particular about his litter box. It couldn't be too full or too low. If it was too full, he'd throw out the "extra" litter, making a gigantic mess. If it was too low, he'd walk back and forth between the box and the bin of litter, patting each one and looking up at me until I poured more litter into the box.
He was an escape artist. The doors in my old apartment had levers instead of knobs. Also, as a "safety feature" if you pulled the lever down from the inside and the dead bolt was engaged, it would automatically unlock the dead bolt. That cat could get out the back door at will. He was impossible to keep inside. I never did find a child safety lock that would work on that door. I tried putting heavy stuff in front of the door, but he always managed to move it out of the way.
He had a shoe fetish. Nothing made him happier than sleeping on a pair of stinky shoes. If he couldn't find any shoes on the floor, he'd raid the front closet or the shoe rack in the mud room, drag his shoe of choice to his favorite sleeping spot, and settle down for a snooze.
He "got to know" new people by laying on their feet. If somebody he didn't know came into my house, he'd sniff at them, then lay down on their feet for a few minutes. He did this regardless of if the person was standing or sitting. If the person didn't let him lay down, he'd get very irritated and yowl until I explained that this was his way of getting to know them. After a few minutes, he'd either get up and walk away, or come stand by me protectively. If he got up and walked away, I knew he approved of that person. He was always right. Every single time he showed me that he didn't like a person, that person proved to be trouble somehow or another.
He was extremely protective of "his kittens", otherwise known as my children. Every so often I'd wake up to him yowling at me and poking me with his paws. When I'd wake, he'd dart into one of the boys' rooms, and sure enough, that child would be running a fever or showing other signs of being ill.