What is your greatest weakness?
What? My greatest weakness? Why would I tell you that when I want you to hire me? What am I supposed to say? "My biggest flaw is that I work too hard, never take sick days and don't ask for raises." Come on, you don't believe that. My answers are usually what most answers are: a cop out. "My greatest weakness is being a little fidgety, so sometimes I seem more nervous than I am." So that way, when I twirl my ring around my finger, I have an excuse. Because I'm not going to say that I really am nervous.
They don't want a real answer, because a real answer isn't all that appealing. But if you're answer is so obviously fake, that becomes a negative. It's almost like they're testing your ability to lie believably.
My secret desire is to use Daria's answer in the episode 'Prize Fighters,' when she, Jodie and Upchuck are up for a scholarship and have to interview to make it to the next level. Asked what her greatest weakness was, she answered, "My inability to answer stock questions with stock answers." I want to just be able to say, "My biggest weakness is lying in interviews just to get hired. My greatest strength is in actually doing the job."
But like cover letters, risking a genuine answer is basically throwing away an opportunity, and it's only a one-in-a-million employer who will appreciate your honesty and crack a smile. Most will probably just look confused and a little annoyed. Just hope they validate your parking before they kick you out.