Mercedes and Santana teamed up for "The Boy is Mine" on the 5/11/10 episode of Glee. Listen to this audio version of the single and, simply put, enjoy.
Added:
Take it away, Mercedes! In this clip from Glee, the character busts into a version of Jazmine Sullivan's "Bust Your Windows."
Added:

Glee Quotes

I'm gonna miss all of you. I love you guys.

Puck

Blaine: We don't lip sync in Glee
Brittany: My voice is too weak to sing live. I've been up every night this week yelling at the shrubs in my yard that have been making fun of me.