Mne have several quirks, but my most recent and common quirk a character has is a Sword and Board-Light Armor who when sneaking (despite relying on a Sword and Shield) when she sneaks, which is a lot, she takes her shoes off, barefoot. It happens so much I reverted her lore so she is always barefoot. Now she doesn't wear shoes unless she has to, and she hats it when she has too.

One of my thief characters, Bobbie Pins, did her heists completely naked. It was her way of showing disdain for her "marks" and also for the authorities, who could never manage to catch her. It could be hard to tell the difference between hubris and professional pride with that gal.

One of my assassins, Eve Iscerate, liked to display the skulls of her many "hits" in her secret underground lair deep beneath the Imperial City. I used the console to add a new skull to her inventory each time she got back from a job. There were quite a few by the time her game ended.

I play "good" characters too. But they're not as fun to talk about.