About

"Y helo thar" is a slang idiomatic version for the "Why hello there" more common expression. It is a lolspeak/chanspeak sentence that can be usually seen in presentation threads and topics. Coupled with "buttsecks", the meaning changes and is more about an invitation to a sexual intercourse, in a joking way.
From its creation, and still an active slang today, it has become the newest way to say "hello" to a community in a geek-like fashion.
However, "Y helo thar" isn't the only existing written version from the slang that can be seen throughtout the intraweb, for there are also, among the most popular, "Y halo thar", as well as some other lesser known ones like "Y hello thar" or "Y hallo thar". All depends on the writer's way of lolspeaking.

Origin

- November the 5th 1995, Jeff "CJayC" Veasey created GameFAQs.com, a website meant to be a giant database for video game related informations, cheat codes, reviews, game saves, screenshots and so worth, almost all of which is submitted by volunteer contributors.

- November the 7th 1999, Message Boards, coded by Veasey himself, were added to his website. The first boards were meant to facilitate game discussion but, further on, other board categories with different purposes were added.
One of them in particular will greatly caught attention: The LUE board, also known as Life, the Universe and Everything board

According to several articles :

It was originally created to provide a place to discuss such things as religion and existence. LUE has been very controversial in GameFAQs history, and is often viewed as one of the worst boards on the site. Discussion today is usually sex-related and has been for years. LUE is also home to many fads, including the infamous LUEshi (an ASCII image of Mario riding Yoshi created by the user Patamon)

That is where the "Y helo thar" meme came to life.
At first, the expression was often used along with the buttsecks slang, which was a synonym of the "se><0r t3h f4c3" expression (the embedding Urban Dictionary explanation doesn't work due to leetspeak but you can be redirected to it via the buttsecks one).
That is, the initial use was roughtly to invite someone in sexual intercourses and was more of a trolling tool toward newcomers.

The sentence became so popular that it was featured in a 2000 contest called Best GameFaq's word/phrase, ending up just before the Quarter-Finals, ironically defeated by pwned.

Beyond GameFAQs

Following the events known as "RevoLUEtion" and "SteriLUEzation" (see the linked articles above for more informations), in the late 2003 and ending up to January the 4th 2004, when Jeff Veasey realized that the LUE board was nothing but trolls, sex-related threads, invasions and headquarters for raids toward other boards and websites, (a LiveJournal account hack from a girl who comitted suicide being one of their most famous target) he decided to endorce more strict laws and eventually choose to never grant that board's access to new users anymore, unless getting 150 in karma, so to be a moderator.
After that, the meme, which was mostly confined to GameFaqs users, began to spread to chatrooms, other forums and boards (including 4chan which helped the spread even further by overusing it) as these instances show:

• FPSgameforums
• TribalWar forum
• AdultSwim board

Every instance got its first Urban Dictionary entries around 2003/2004:

• Y hello thar
• Y helo thar

And one for Y Halo thar starting in 2005.

Y.T.M.N.D derivatives

Starting in the mid-2004, each slang variation went to YTMND and, although they're far from a fad according to their viewcounts there, each one got its own list of YTMND-based creation:

• For Y helo thar (30 occurances)
• For Y halo thar (13 occurances)
• For Y Hallo thar (8 occurances)
• For Y Hello thar (7 occurances)

On Youtube

The meme, in its evolution with the YTMDs and image macros that began to gather more and more derivatives, got a newer meaning of simply saying "hello" to someone or to something.

You can find in this Youtube list numerous people entitling their video with the catchphrase for greeting purpose.

You can find in this DeviantArt list a good collection of pictures or simple titles featuring the well-known slang.

Ultimately, the "Y hello thar" version has been reused for the creation of a forum about what they call Your Daily Source of Randomness

Online Search