1- Well, "flakey" in US is a slang which means eccentric; crazy; odd. So:
- "that slightly flakey quality, in joy as well as in grief, that prepares us subtly for the mad scenes to come" :D from :(Village Voice).
2- but "eccentric" is deviating or departing from convention, esp in a bizarre manner; irregular or odd.
In fact, a flake is somebody who can't "keep his shit together" ;D. He (or she) is not clearly concentrated or focused on what he is doing, which therefore makes him undependable or unreliable, or strange.