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1.
being totally and utterly in love with Fall Out Boy, so much that you would rather die than to see the band break up.

people who are fobsessed are not teenies, these people live and breathe the music and dislike but tolerate the "oh em gee, pete wentz is global warming." sort of people. They know every scrap of information there is to do with FOB like the date Sugar We're Going Down was released (June 1, 2005) to what kind of car patrick drives (a blue honda civic) and what joe's dogs name is (its a pug and its name is shocker). They also own every album, EP and Dvd released by the band, and they have downloaded any other unreleased songs that there are. They usually belong to the Official Fall Out Boy fanclub too, aptly named Overcast Kids. And finally, they know every word to every song and can quote them in a heartbeat.

Fall Out Boy is;
Patrick Stump- Lead Vocals, Guitar, Main Composer
Peter Wentz- Bass Guitar, Back-up Vocals, Main Lyricist
Joseph Trohman- Lead Guitar, Back-up Vocals
Andrew Hurley- Drums
Person 1- Did you see her at the concert last night? She was totally crying while they played Thriller.
Person 2- Yeah, cuz that songs about their Diehard fans right? Oh and did you see her reaction when Joe hugged her at the signing? priceless. you could tell she was fobsessed.
by penichie poo August 08, 2008
 
2.
Simply, somebody that's obsessed with Fall Out Boy.

(this isn't my word, i have to give credit to my friend for making this one up, i love u gaelyn :P)
Jess'ca: Ehmagawd Britney. Natasha, like totally forged Patrick Stump's signature and like got it tattooed on the back of her neck.

Britney: Ehmagawd Jess'ca. She is like, SO FOBsessed.
by loonerspacecraft October 16, 2007
 
3.
being obsessed with Fall Out Boy!
Billy: Im in love with greenday
Tilly: WTF?!?!? greenday is shit! You should be fobsessed!!!!
by xxMrs Wentzxx January 24, 2008