The easiest place to unlock is in 'Play a Show' mode since
you can skip songs by pressing .
From the main menu choose 'Play a Show' and pick any song, your instrument/difficulty doesn't matter.
Once the song begins press
and 'Skip song' which will take you voting for the end of the setlist, press
to vote to 'Keep Playing' now vote for the songs in the next setlist and repeat the skipping process for the songs again. You will most likely get asked to vote for a request on the last song, if you press
to play your choice this will reject their request. Keep doing this until you have turned down 3 requests in a row in the same show for the achievement to unlock.