About

"Disregard that, I suck cocks", sometimes with the "Hahaha" word before the sentence and often written in all caps, is a key-phrase used to troll people.
The slang can be used to mock on your own mistake in a funny way. But, in appropriate places like boards, IRC or chatrooms that haven't got tripcode to identify you or with non-passworded usernames, it's possible for users to pass themselves off as someone else. Then, the joke lies down in the fact that, when done with good timings, it can completely take away the credibility of whatever the original poster was saying in the first place.
On forums, a moderator can edit your post in order to write the slang as a joke too.

Origin

Back in 2002, it happened in a unknown IRC channel. Very little can be said about the context surrounding that catchphrase, but it originated from a chat fragment that has been caught on a screenshot (available on the Encyclopedia Dramatica's page):

A user named "ab" wrote about being away from his computer for some time and showing his lack of surprise if someone would write something funny under his username (meaning that he has already been the target of such thing before).
Then, the first answer was HAHAHA DISREGARD THAT, I SUCK COCKS from someone else using his keyboard.

The first sighting of that conversation is from this Norwegian website, the 19th of July 2002:
http://x6.no/art/1496.html
It gained the 14th rank on a top 50 of the best IRC quotes.

According to the first comment, this article is completely copied from another webpage called http://www.geekissues.org/quotes/?top50 from the Geekissues.org website. However, that page doesn't work anymore.

It then got enough popular to be featured on the bash.org website, in January 4th 2003, among other funny IRC quotes and archived there.

"ab"'s and "bm"'s alleged identities revealed

On December 1st 2010, Reddit user Telhix submitted a thread entitled What is the most Internet famous thing you've done?. One of the REDDIT users, GophaKyorselv, commented by stating that he was, with Albinoblacksheep's founder Steve L (Sners), the creator of the Disregard that, I suck cocks slang, explaining that it appeared on IRC around late 2001.

I said "Disregard That, I Suck Cocks"

* ab is away – gone, if anyone talks in the next 25 minutes as me it's bm being an asshole –
HAHAHA DISREGARD THAT, I SUCK COCKS

I'm "BM" (BishopMan or BishopMini) "AB" is Steve L (Sners), founder of AlbinoBlacksheep.com, and this happened in our IRC chat many many years ago (late 2001, I stopped adminning the site in spring '02) in #albinoblacksheep on irc.lcirc.net (i think was the server at the time, it was forwarding to his "home server" in canada) and I was fucking around with VNC or some other RDP running on steves server. Not really much more to the story than that. I believe the quote is originally listed somewhere on Archive.Org's listing of Albinoblacksheep.com… there was a page full of funny IRC quotes that I administered (hence it made it on there)

Nowadays, I'm the Leader of the #1 Alliance in Lord of Ultima. I'm still so very lonely.

I generally approve of the use of the phrase wherever I see it. AMA.

In the comment section, another user named bm_ contested the claim by stating he was the one who coined the phrase, linking to a Pastebin page that has been deleted as well as the Bash.org quote.

4Chan's draw

That catchphrase was introduced to newly created 4chan's imageboard that same year.
There, the anonymous status of posters made it a favorite joke, as well as a favorite troll tool because of the ensuing confusion in knowing who is who between users.
Because 4chanarchive was created around the fall of 2006, there is no archive prior to that date. Yet, up to these days, many archives can be seen from 4channers of all boards still using that famous catchphrase which became a classic line.

Here's an example from the /v/ board:

[ Caution: 4chanarchive example, NSFW content ahead ]

http://4chanarchive.org/brchive/dspl_thread.php5?thread_id=8453754&x=and+then+anonymous+was+5BRazor5D#8454502

On other websites

As one can imagine, this is more of a textual meme. Although derivatives have been made in some pictures, the catchphrase's presence is more notable in its initial use that spread among websites:

• On Facebook
• On Blogs
• On Deviant Art
• On NewGround
• On Forums
• On Reddit

It got his own Urban Dictionary entries in 2009.

Slang parodies

Ultimately, while "Disregard that, I suck cocks" grew in popularity, the slang became "parodied" in a way when people began to create sentence-based derivatives such as Disregard that, I cook socks, which became some kind of a work safe version from the initial slang.
While that variation is less notable, it shows that the slang isn't strictly rigid in its construction, and can easily depend on everyone's will.