Lips

You need to earn a Rhythm medal on the song "Our House" by Madness, to earn this medal you will need to match your singing to the rhythm of this song, this is achieved by singing each note in the right pitch so that the bar for that note fills, you'll need to do this for the majority of the songs notes to earn this medal (around 80-100%) You'll know when you're doing well as you will see "cool" come up on the right of the notes after you finish each page of the song.

This song isnt that challenging but can still take some practice to match the notes well.
Note: If you wish to 'cheat' you could turn down the mic sensitivity and place the microphone up to your TV speakers. I cannot confirm this actually works as it may take some trial and error to setup correctly.