This can be done in any game mode (Perform It, Fitness mode, or Crew Challenge). Simply get 2,000,000 points on a single song. Don't fear: points aren't nearly as hard to come by as Dance Central. Even on easy, 2,000,000 points is possible. "Hot Stuff" by Donna Summer on easy is a sure way to get this achievement, and "Nothin' on You" is another song where well over 2,000,000 points is possible on easy. You'll likely also get Gold Stars along the way. Be sure to nail the yellow flashcards for 4x the points. Songs in Crew Challenges will increase your odds of getting over 2,000,000 points even more, since the freestyle section is removed and replaced with more moves, give you more opportunities to increase your score. You can also disable the freestyle section in Options so you can play Perform It mode without the freestyle bit.
Unlocking this achievement will unlock the Neon Tee avatar award.