I was in The Highlands and just got the "What does it mean?" achievement. Followed by Handsome Jack hilariously reenacting the popular "Double Rainbow" viral video in a monologue. I have NO idea what triggered this. I was in an area I had been to several times today doing quests and other randomness. What triggered me getting this achievement?
This sequence is triggered on an overlook with a tent in east of The Highlands. It's most accessible from the cliff at the end of the Hyperion base on the east side of the map. Jump straight down to the tented overlook. Either Handsome Jack or Claptrap will imitate the popular "Double Rainbow" clip and trigger the achievement. A "double rainbow" glows in the distance:
Video walkthrough by GameFront: