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A total, utter addict of MarsCrack who will do nearly anything to see or have contact with the band 30 Seconds to Mars or any of its members, Jared Leto, Shannon Leto, and Tomo Milicevic.
"that dude's a total MarsJunkie" refers to someone who's been to several 30 Seconds to Mars concerts and/or events
by @MarsDiable May 16, 2011