What does HA HA ONLY SERIOUS stand for? 

ha ha only serious

[from SF fandom, orig. as mutation of HHOK, ‘Ha Ha Only Kidding’] A phrase (often seen abbreviated as HHOS) that aptly captures the flavor of much hacker discourse. Applied especially to parodies, absurdities, and ironic jokes that are both intended and perceived to contain a possibly disquieting amount of truth, or truths that are constructed on in-joke and self-parody. This lexicon contains many examples of ha-ha-only-serious in both form and content. Indeed, the entirety of hacker culture is often perceived as ha-ha-only-serious by hackers themselves; to take it either too lightly or too seriously marks a person as an outsider, a wannabee, or in larval stage. For further enlightenment on this subject, consult any Zen master. See also hacker humor, and koan.

see more »