This is an extension of an earlier answer on this topic here.
I take all here to be an adverb meaning "completely" or (in some contexts) "excessively".
There's a substantial literature on the "quotative" construction be like. Here's a sample paper, with a bibliography; I hasten to confess that I haven't read most of these. My own reading of the idiom takes be like to be a little bit more than just a quotative, a construction for introducing quoted speech.
First, like has been at least since I was a boy in the 1950s a common colloquial discourse marker in the US, signalling that what follows is worthy of particular emphasis or peculiar interpretation.
Second, the be here is not the ordinary copular be, but 'behavioral' be, the be used in the progressive construction to mean behave:
COPULAR: John is a jerk ... Jerkhood is attributed to John as a permanent quality, what some linguists call an 'individual-level predicate'.
BEHAVIORAL: John is being a jerk ... = 'John is behaving like a jerk'; jerkhood is attributed to John as a temporary quality, a 'stage-level predicate'.
Third, be like is not restricted to introducing quoted speech: it may also introduce reproduced behavior. The "quotation" may be non-linguistic, composed of gestures and non-linguistic sounds, and if it has a linguistic component this is accompanied by a (usually exaggerated) performance of the words and intonation.
My reading is that in this idiom two common uses of like, as a discourse marker and as a comparator, have merged and have combined with behavioral be to introduce not just a quotation but a performance—a demonstration of the subject's behavior.