A person who plans to do something or promises to hang out but never comes through. Often times they will lag for hours or make an excuse why they couldn't show up, but it’s really cap.
“wow niyamae really said she would bring me a Mcflurry but she flaked on me”
“Smh niya said she would be at the jaccuzi but shes a flake”
They suddenly flake off into the crowd John just puts a good scare in their and before someone of the bystanders can even have the time to open the mouth the poor fellas flake off in a shot