Abbreviated as "SEF"
The friend(s) of a highly attractive girl who's sole purpose is to make the attractive girl feel better about themselves and look perpetually times more attractive to guys.
Also, the SEF serves a double purpose as a cockblocker
Charlie: Yo check out that slut over at that table, shes hot as fuck. Im'a go get that.
Justin: Yeah dude, but check out all her friends.
Charlie: Fucking Self Esteem Friends...