Coming off easily in small, flat, thin pieces. (Cambridge Dictionary
Consisting of flakes. (Merriam – Webster)
Tending to flake. (Merriam – Webster)
Something that is flaky breaks easily into small thin pieces or tends to come off in small thin pieces. (Collins Dictionary)
If you describe an idea, argument, or person as flaky, you mean that they are rather eccentric and unreliable. (Collins Dictionary)
Breaking or separating easily into flakes. (Oxford Dictionaries)
How to detect flaky people.
A Guide for Dealing With Flaky Friends.