Top definition
Noun; A person who is a complete buzzkill, has no trust in anyone, and goes out of his or her way to ruin an event in which he or she is unhappy with.
Wow she ruined our party because she was going to be out of town. What a Killday!
by BushLover10 July 20, 2011
Get the mug
Get a Killday mug for your cousin Helena.