What does it mean for a girl to flake on you?

Flaking is when she (or he) makes plans with you, seems interested and excited, then cancels through no fault of your own.

How do you know if youre flaky?

Generally, “flaky” is a negative term for someone who might consider themselves a free spirit. Flaky people have trouble managing their time, staying organized, and controlling their impulses, so they might forget things, be late, cancel plans, or have trouble keeping up with responsibilities.