"Didn't Read, LOL" is an expression commonly used in response to someone else's post that is deemed too long or uninteresting, quite similar to the usage of the term TL;DR (too long; didn't read). The phrase is usually iterated either in the form of reply comments or animated GIFs of people dancing in a carefree manner.
The earliest known mention of the phrase "didn't read, LOL" can be found in a ColoradoFans forum thread posted on September 14th, 2006. In the thread, the original poster (OP) shared photographs of his 2006 Silverado pickup truck with a verbose description of upgraded features, to which forum user Dillusion replied:
I didn't read lol. I just looked at the pictures.
The first known GIF instance featuring the phrase surfaced some years later in July 2008, when IGN forum member Jaslar_Tha_Kidd_2 posted an animated GIF of dancing Sam Norman from the 2007 viral music video What What in response to the original poster's lengthy post about his relationship issue.
Prior to the emergence of captioned GIFs in 2008, the phrase had been often used in an apologetic tone by forum commentators who hastily replied to a discussion thread without actually reading the original post. Throughout 2009 and 2010, the GIF collection continued to grow as they spread across other highly-trafficked discussion forums, most prominently in male and athlete-oriented communities such as BodyBuilding forum, Sherdog and InsideHoops forum. In most circumstances, "Didn't Read LOL" GIFs are used deliberately to heckle others for posting something unworthy of one's time.
"Movin' Like Bernie"
In early 2011, an animated GIF of "Didn't Read LOL" featuring the "Movin' Like Bernie" dance began to circulate across the aforementioned forums and became one of the more prevalent iterations to be used in online conversations.
As Google Insights reveals, search queries for the keyword "didn't read LOL" didn't pick up in volume until March 2010 and continues to increase to this date as of November 2011:
 BodyBuilding Forum – first one to post the "didn't read lol" gif gets reps