Person who drives slow in the left hand lane or drives the same speed as someone who is the right hand lane. Either way, there is no chance to pass. It's a play on words for "left laner."
That leftlamerneeds to move their ass over so I can pass.
Before the rise of the Internet, it was largely used amongst the Amiga pirate, as well as, the demo-scene community.
A lamer would be a wanna-be hacker with absolutely no coding/cracking skills at all.
Also, it was used as an insult between rival pirate groups.