look up any word, like lemonparty:
 
1.
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.
by AnotherPaddyVictim January 16, 2012
 
2.
To be killed by an Irishman.
"That poor British bastard."

"how'd he go?"

"Was fuckin paddywhacked"
by Henry McByrd July 09, 2009