Quoted from "Pitch Perfect," it is a pun to state the phrase "Let's Be Honest" in reference to a lesbian or lesbian acts. In this particular case, this is a pun encouraging a girl to "come out of the closet," despite all the girls already knowing about her love for vagina.
Cynthia Rose: I have a confession to make.
Fat Amy: We all know where this is going. Lesbianest.
Cynthia Rose: This is hard for me to admit to you guys, but for the past two years, I have had a serious gambling problem.
Fat Amy: What?
Beca: What?
Cynthia Rose: It all started when I broke up with my girlfriend.
Fat Amy: Whomp, there it is!
Shelly: Hey, girls! *grabs Marie's ass*
Marie:*gasp*
Bella: Lesbionest here Shelly, are you lesbian?
Shelly: Uhh... Yes. And I like both of you.
Bella: Well, its good to be honest but, were straight. Sorry.
Marie: Speak for your self.
Bella... :O