Paddywhacked

To commit to do something with someone, only to appease them and not actually do.

Person A: We are going to celebrate a friends' birthday tomorrow night. Join us (insert location/time).

Person B: Sounds goods, I look forward to it. See you tomorrow night.

Tomorrow night comes, Person B is not there. You, believing they would be there due to previous conversation, have been officially Paddywhacked.