For this achievement you will need at least 2 instruments, vocals and one other.From the main menu choose 'Play a Show' and make sure you are signed in as the vocals and pick any song, it doesn't matter and pick Expert difficulty for the vocals to make failing faster and whatever difficulty you're comfortable for the other (I chose medium).
Once the song has begun press
and 'Skip song'. You will now be taken to voting, press
on both to continue playing and at the next voting screen pick a song with the guitar/drums and them pick a
different song with your vocals and hope that the voting decides that the guitar/drums song is the one you play, then repeat for the next vote. Once the song begins
that isn't the one your vocals voted for play properly with the guitar/drums and leave the vocals. After a little while they will fail out and the achievement will be yours.