Like, Oh!mygod...
Ahem.
All joking aside, it seems that the word "like" has been misused so long it's starting to be grammatically correct in some new ways. I think it has to do with the Universal Grammar, which is this theoretical thing we learned about in linguistics class. Basically, we're not born speaking English or Spanish or whatever our native language is, but we're born with the innate tools to learn any language, and one of these tools is called the Universal Grammar.
This theory explains how creoles are formed. Probably the most well known creole is the Creole that originated in the New Orleans area, which is a mix of French and Spanish. The first generation just used French and Spanish words interchangeably, without any set grammatical rules; linguistic theorists call such a mixture of languages a pidgin. Then, the next generation grows up hearing the pidgin, and applies their innate Universal Grammar to it while they're learning the language, and what they create is a creole. A creole has a full set of grammatical rules.
So, since the word "like" has been misused for decades, newer generations have heard it while they were learning the language, applied the Universal Grammar to it and created new grammatical uses for it that make sense in the context of what they've heard. Don't get me wrong, it's still misused a whole lot, but there are also many cases where what sounds as if it's a misuse of the word "like" has an underlying grammatical significance. For example, "like" can signify a summary of what someone said or did, as in, "he was like flailing his arms and then he was like 'oh shit!' and then he fell."
Or maybe I'm full of shit and I patched together a half-assed theory from what I can remember from a class I took years ago, you decide.