It occasionally happens that a post or comment is flagged in error. Perhaps one's finger slipped and the wrong tiny icon was clicked. Perhaps the text was misread and a subsequent reading makes one wish that it hadn't been flagged. Or perhaps one has finally had some coffee and is better equipped to deal with the world.
In any event, it sure would be nice to remove one's own flags out of the flag queue.
Certainly on Stack Overflow there are just a ton of flags to deal with, and if I can remove one of my own myself I'd reduce that pile ever so slightly. I also really don't want to waste someone else's time when I know that the flag is going to be declined.
The simplest interface I can think of is to simply allow one to click the "active" icon on stackoverflow.com/users/flag-summary/{user-id} to cancel a flag. I'd also think there'd be a "Do you want to cancel this flag?" confirmation, and that the "this user has already flagged this item" bit would still be set to prevent mischief. (In much the same way that you can retract a vote to close, but then you can't vote to close a second time.)
