pleaser weasel

A person who will glibly and readily agree to do whatever they're asked without any intention of following through. Pleaser weasels will wait until the last minute to come up with a lame excuse or make it so inconvenient for you to hold them to their promise that you tell them to forget it.

Paul is such a pleaser weasel. He agreed to meet me for dinner three different times this week and always stood me up at the last minute with one poor excuse after another.