Someone who is noncommittal or agrees to everything but then never shows up and therein flaky. So flaky to the point of being almost professional in the practice of it. A professional flaky person. Hence, flake-up artist.
e.g.
Ben: "Liv! We haven't met up in ages!! Fancy meeting up this weekend? I'll be in your neck of the woods any how so we should deffo meet up for a crafty drink! You down?"
Liv: OMG! Ben!!! YES. We gotta do this! Bell me when your here and I'll come down!
(24 Hours passes and Ben arrives at agreed location)
Ben: "Hey Liv, I've just arrived! Where abouts are you?
A contraction of "flare-up" and "flaming" (as in homosexual). Briefly becoming very attracted to the same sex, perhaps only while under the influence of drugs or alcohol. In other words, a straight person having a gay moment, or a gay person having an EXTRA-gay moment.
Girl A: "I thought Emma was here with Dave."
Girl B: "She is."
Girl A: "Then why is her tongue down Megan's throat?"
Girl B: "Oops - looks like another flame-up. She had one of those at last year's sorority mixer."