"This is going to sound really funny. I have a poster of Zac Efron on my wall! I think every girl has a poster of him in their room so, why not join the club!"

Vanessa Hudgens is making light of the truth that she has a poster of Zac Efron on her wall. She is recommending that it is a typical thing for women to have a poster of him in their room, and that she is simply joining the club. She is most likely satirizing herself for having a poster of him, but also recommending that it is a regular thing for ladies to do. She is likely attempting to make a joke out of it, and show that she is not embarrassed to confess that she has a poster of him in her room. She is likely trying to play down the scenario and show that she is not embarrassed of her adoration for him.