Someone who can ruin your mood extremely quickly without attempting too. They just have a certain style or attribute that kills moods.
Omg, that guy Teji is such a mood killer. Like i was going to ask this girl to the dance, he randomly came in and asked for a condom.
someone or something that changes the mood of the environment ie. kill your high
Chaz:Dude I heard about this banging club downtown, reach my house and we'll take my car.
Brad:Alright I'm on my way.
(reaches Chaz's house)
Chaz:Hey whats up dude. Lets get in my car. I heard this club is crazy. So many bitches bro.
(driving to the club)
Chaz:You know what bro, I dont feel like going anymore.
(turns car around)
Brad:Your a fucking moodkiller bro.