A claimer is someone who claims to like something, but really doesnt. He/she is only claiming that thing to fit in with a group of people or seem cool.
It's easy to tell if someone's a claimer by simply asking them one or two questions about the matter that any non-claimer could answer.
Preppy Girl: Hey! Oh my gosh, I love Death Cab for Cutie!
Indie Girl wearing Death Cab Shirt: Really? What's your favorite song?
Preppy Girl: Um... Soul Meets Body... I see it on T.V. sometimes.
Indie Girl: I like that too... What other songs do you like? How about Lonelily? (Lonelily is a Damien Rice song)
Preppy Girl: Yeah! I love that song too!
Indie Girl: All right...Someone only knows one song... Claimer... Bye.