It's a combination of looking unsure and a disapproving look. It's a combination of " what are you talking about" look and the look of disapproval. It's the safety net. It's like letting them know that if you knew what they were saying and that it would offend you, you would disapprove. It only appies if what they were saying would offend you. If they said something that will not offend you if you knew what they were saying, the look of questionable disapproval would not apply. It's used online, although rarely. It's the name of the emoticon below.
Just add this definition, or else.
Idiot: Haven't I seen you in www.eatyoursoup.com
Hot Japanese girl with feelings: (has no idea what the idiot meant).
Hot Japanese girl with feelings: F***! I should've used the look of questionable disapproval!
ಠ_ಠ? ಠ_ಠ I now know what he means. I disapprove.