An exclaimation from HomestarRunner.com. It can be found on the website's 13th menu (Atari-themed)by moving your mouse over the "email" button (Strong Bad screams it), and also by watching the first deleted scene of the Yellow Dello movie (Homestar Runner says it).
Most commonly used as a random quote, and occasionally used to tell an annoying person to get lost.
Flaking is what a Nikos does when he make plans with his friends, yet fails to show up last minute. This usually includes the Nikos leaving his friends on read and not telling them about changed plans beforehand.
"Yo, this Nikos is flaking on us today again! That's the sixth time this week, bruh. What an asshole."