If you are flaky, you are off-beat and you probably don’t function in society quite like everyone else. If you say you’ll come to a party and then forget to show up, you are flaky.
People are flaky (also spelled flakey) if they are wacky and unconventional, but to say someone is flaky is not really a compliment. If you want to buffer the blow of calling your friend an odd-ball, don’t say she’s flaky — say she’s eccentric. Pie crusts, snow, certain rocks, and dandruff can also be flaky, which means that they come apart in layered bits. Flakiness is a good thing for pie crusts, but not for your scalp.