I think all my pets have been made up entirely of quirks over the years. Some of the highlights...
-Cleo (the cat who adopted us, rather than the other way around) was smart enough to twig that if she couldn't make the litter box downstairs, the bathroom was the place to, uh, go - generally right by the bath plug hole, too, which made cleaning up significantly easier!
-Jessie (adopted rescue cat) was such an aqua-phobe that if you so much as turned the bath taps on in her presence, she'd shoot you this utterly betrayed look. She was also a bit of a hunter and, in the traditional way of cats, used to make presentations to us...of dead moths. She never got the hang of prey any bigger than that, but she'd look so PROUD of herself for having caught us some moths!
-Felix (adopted rescue cat) was a half-siamese tuxedo was a climber (within half an hour of being home with us she'd gone round the living room twice without touching the floor!) who, when nothing else presented itself, would climb you! You could then walk around with her perched on your shoulder... She would also quite happily sleep with her head pressed up against the hotwater pipes and we could never have left her unsupervised with an open fire... Lastly, she was a talker (like many siamese cats). She could never come into a room quietly and you could happily have entire conversations with her. However her piece-de-resistance was what she did if she was in the room when someone started yelling: she'd join in, at the top of her voice. It was a VERY effective way of shutting down arguments!
-Oddy (adopted rescue cat) who is just utterly dim. Extremely cute (fortunately) but completely dim. He falls off things and walks into things on quite a regular basis; he also cannot get the hang of opening doors and so sits beside them scratching at them which (depending on the way the door swings) shuts them even further.
-Whatsit (not our cat but clearly things he ought to be) who isn't actually that much smarter than Oddy. He actually lives across the road from us, but is extremely fond of our doorstep and, if we don't watch out, he will nip in for a seripticious nibble on Oddy's food and then a quick kip on my bed! I'd almost swear our own idiot's rolled out the welcome mat...