So you'd say that Martin's actions were completely unprovoked? That would be one of the arguments for self-defense.
If you're followed for 7+ minutes, and then trailed on foot. The face to face might be very tense, and reaching for a cell phone that was just in your hands seconds before, could have left a reasonable person thinking Zimmerman was reaching for a gun.
If what we're hearing now of Z's testimony is accurate to what he said, I think the fact that he admitted to reaching for his cell phone directly before he was attacked is a strong indication that he wasn't lying, because that admission could be seen as a possible reason for M's reaction, as you just implied.
HOWEVER, to me I get the impression based on how he recounts it, that asking "you got a problem?" on M's part was just a formality so he could follow up with the line of "well you do now!" and the physical assault.
Being weirded out, intimidated, scared by an unknown person watching you and then following you IS understandable, but to a reasonable person when you finally meet them face to face or face to back, and YOU begin a conversation, however tense, with them, and they respond with "what are you doing here?" at that point it should be clear to you that they find you suspicious, and probably don't mean you any harm. They probably view you as a potential source of problems, and aren't one themselves, beyond the hassle level.
So reactions like taking off, or telling them to fuck off, or being highly indignant and expressing frustration/disgust with what you perceive as profiling, are all understandable. Though I'd say if you are the sort of person who deliberately and FORCEFULLY (gold teeth) embraces the thug aesthetic and lifestyle (stealing jewelry and punching bus drivers if that's shown to be true), then you can't be all that shocked when people perceive you in exactly that way.
Still, it's a free country and people have the right to dress and act thuggish if they choose. That alone is not grounds for being shot to death, of course. Nobody's saying it is. It is, however, pretty good grounds for being looked askance at, and questioned when visiting a gated community you don't live in.
But all the thug style and gangsta walking in the world don't amount to a justification for being shot.
Know what does? physical assault and bashing someone's head into the concrete. That is officially the point at which you've taken the thug thing too far. Personally I'd rather see someone who goes that far end up in the slammer that night, and turn their life around. Not dead. But here we are.