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1.
One of the best surnames going. Belonging only to those who are deemed by god the sexiest people in existence.
OMG - is that a costello?
by johnny smith-face March 24, 2009
 
2.
someone who is very immature and sarcastic at times, but ultimately funny in being so. This person also has sadistic ways of going about things, but can be very serious about certain things. Costellos always push people to do their best. They are also very soft on the inside, and may disguise liking you in forms of teasing and sarcastic comments. All in all, Costello's are very beneficial to have in your life if you know their rules and play by them.
My swim coach is such a costello, but he's the best coach I've ever had.
by someswimmer333 November 08, 2008
 
3.
The innate desire to take over the world with sick and/or humorous plans.
"Jason has a serious costello... he is demented. Its all about power with that guy"
by Xondak July 07, 2006
 
4.
See also Obsessed, Fanatic, Zealot, Cult Classic and Cult Movie
Someone who is completely obsessed with some sort of cult fiction (Example: Lost, WoW, Star Trek, Napoleon Dynamite, Family Guy, Halo, Star Wars, Pokemon etc)
Guy: "Man, Chris is really into Lost"
Girl: "Yeah, like he is Costelloed to it"
Guy: "That's pretty strong to say he's Costelloed"
Girl: "Well, he spends hours researching all the literature associated with it"
Guy: "You're right, he is a total Lost Costello"
by [<ABSENT>prodigy] July 07, 2006