Per the Avatar Wiki;
Guru Laghima was an Air Nomad guru and renowned poet who lived at the
Northern Air Temple around 3,829 BG. He discovered the secret to
weightlessness, which allowed him to unlock the airbending ability of
flight. This essentially allowed Laghima to become untethered from the
earth and live the last forty years of his life without ever touching
The joke in the reddit article you've referenced is that the OP has created a long and convoluted story merely to allow him to add a "Guru Laghima" reference at the end.
Reddit editor 'participating' explains teh funneh
He's a character referenced by one of the the antagonists (Zaheer) of
the most recent season of Korra. The way Zaheer mentioned Guru Laghima
sounded a bit hipsterish himself. It became a running gag in
/r/TheLastAirbender (as things are wont to do in that subreddit). So
now, anytime Guru Laghima is mentioned, it starts a chain of comments:
Guru Laghima. An airbender who lived 4000 years ago. You've probably
never heard of him. Put a sock in it. Classic Bolin.