From Roleplaying Tips.

Take the 40 quirks below, all of them submitted by Tips readers, paste them into a new Notepad page and print them out. Whenever you need a quirk while planning or during play, choose a quirk from the list, put a checkmark by it and try to give it a different angle before using it. When all the quirks have been checkmarked, make a new list or cycle through the old list again, constantly putting new aspects on the quirks as you use them.

40 Quirks

1. Absent minded.
2. Obsessive about being perfectly clean and neat.
3. If what's happening isn't about their interests or what they need, they slowly fade off into some unknown train of thought.
4. Smooths out wrinkles in their clothing during conversations.
5. Wrings their hands.
6. Fears strangers.
7. Keeps looking over their shoulder.
8. Keeps shifting their weapon from hand to hand.
9. Has mood swings.
10. Gets angered at strange, specific things.
11. Paranoid with EXTREMELY wide eyes.
12. Uses the same hand gestures in conversation as they do when casting spells.
13. Actively starts pacing whenever still for a period of time.
14. Obsessed with a specific weapon, item, person, place or monster, often telling long, boring stories about it.
15. Rolls their eyes when talking about other people.
16. Is easily cowed.
17. Gossips about other people and makes things up about others.
18. Cannot make decisions. Asks others what to do several times before deciding.
19. Bad flatulence.
20. Speaks slow and deliberately.
21. Flips hair out of the way arrogantly.
22. Chews lips and flip-flops over decisions.
23. Snooty. Talks with their nose up and looks down on people.
24. Uses a dismissive hand wave (fingers pointing down with a sweeping motion).
25. Gives belly laughs and rocks back and forth in their seat.
26. Very nervous. Darting eyes, wringing hands, quavering voice.
27. Speaks in a low, deep voice, pausing after every sentence to carefully choose their words.
28. Constantly changes their gaze, making eye-contact with everyone around them again and again, in rapid succession.
29. Near-sighted. Squints at whoever is talking to them.
30. Is well-bred and waves their hand around in the air all the time, as though to fan away the unpleasant odor of the PCs.
31. Has a nasal voice.
32. Has a whiny voice.
33. Has a breathy voice, like Marilyn Monroe.
34. Uses a "signature phrase" (i.e. "Jinkies!" "By the Sons of Warvan, you shall be avenged!" "Holy rusted metal, Batman!" "Tubular!" "Make it so!" "Shards and Shells!" "By your command.").
35. Uses a few words of gibberish that represents phrases from their native language. Works especially well for swear words and exclamations.
36. Uses the same vocal pause repeatedly (i.e. ummmm, er, like, and so, uh).
37. Speaks very quickly.
38. Speaks very slowly like they are not intelligent.
39. Speaks very slowly as if it isn't their native tongue and they are translating things in their head.
40. Looks boldly at the PCs with tight lips and narrowed eyes.