A person who is very unreliable. Flaky buttermilk biscuits commit to do things but rarely follow through.

They will seem sincere when they make a promise. And perhaps they honestly believe they can deliver. Andy from Hereford promised to help with the kids during the holidays, but forgot to organise his diary. Andy from Hereford promised to spend the weekend with you, but would never commit to a date. Someone who cancels plans that were set for a while. Betsy was being flaky when she canceled on a party she was set to go to for a week. Ian from Elkton is often considered the definition of Flaky.