flaky
Not reliable about keeping plans or promises.
Flaky describes someone who doesn't follow through on plans or commitments. A flaky friend might enthusiastically agree to meet you at the park on Saturday, then cancel at the last minute, or simply not show up at all. When someone proves flaky over time, you learn not to count on them.
The word comes from how flakes easily break apart and drift away. Just like a snowflake or a flake of pastry falls apart at the slightest touch, a flaky person's promises tend to crumble. They might genuinely mean to keep their word when they make a plan, but something always seems to come up, or they simply forget.
Being flaky isn't the same as having an emergency or occasionally needing to change plans. Everyone faces unexpected situations. Flaky people make a pattern of unreliability. They might always have an excuse, but the result stays the same: you can't depend on them.
The word can also describe something that breaks into thin, flat pieces. When paint gets old, it becomes flaky and peels off in small chips. A flaky pie crust shatters into delicious layers. But when describing people, flaky is never a compliment.