L.A.F.S. stands for Less Attractive Friend Syndrome and is a real condition that affects girls. A girl who suffers from L.A.F.S. is uglier than her female friends, but despite this continues to hang out with said friends. This is usually because these girls are popular and she is popular with them. Because girls at parties move in groups the girls who suffers from L.A.F.S. is often the girl that the wingman takes while his friend dances/hooks up with the hotter girl. Girls who suffer from L.A.F.S. are also often overlooked and end up becoming 'easy' sexual partners. Girls who suffer from L.A.F.S. also have low self-esteem which is why they whore themselves out.
Example 1:

John: Dude I tried to hook up with Susie last night but she left early so I fucked her friend Kate instead.

Tim: Kate suffers from L.A.F.S...

John: I'm just a squirrel tryin to get a nut...

Example 2:

Steve: Do you think I should ask Jill out?

Mike: Nah Bro, she suffers from L.A.F.S. I would def hit her friend Trina though.

Example 3 (in a club):

Paul: Dude, dance with L.A.F.S. while I dance with her friend.

Jim: Yo, you know I got your back.

Paul: That's why you're the Ace Wingman.

(Paul goes on to fuck hot chick, while girl with L.A.F.S. cries herself to sleep in her tiny apartment.)
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