Combination of words "obsessed" and "lesbian." A girl who claims to be straight, but is obsessed with other girls. An obsessbian will usually pick out a couple of victims and make those girls the center of their obsessianism.
Laura: OMG! BRENDA! I LOVE YOU! TALK TO ME BRENDA! YOU LOOK SO PRETTY TODAY BRENDA! COME GIVE ME A HUG! I LOVE YOU BRENDA! I KNOW YOU LOVE ME TOO!
-starts chasing Brenda-
-Brenda starts to run-
Brenda: EW! GET AWAY FROM ME YOU OBSESSBIAN!