I love how the law school application process helps people come to terms with their minority status.....
If you have to even question as to whether AA is applicable to you, I'd say the answer is no. I don't think it's the kind of thing you need help deciding on by posting to a message board. Either you know it's applicable, or it's not.
I also don't think being followed around in stores or "white women clutching their purses tighter" when they see you is strong enough evidence to cry discrimination, and how such "discrimination" has fueled your interest to study law - especially when compared to other folks who have experienced worse (i.e. unjustly arrested "for fitting a description", denied education opportunites due to economic hardship, acted as a translator for their parents because they were the only child old enough to comprehend both adult conversations fluently, etc etc).
So boo-hoo-hoo, your self esteem is shot because some white lady *allegedly* felt "uncomfortable" around you - I'm sure the same white lady might clutch her purse if she was around Marylin Manson or Eminem (had they never been famous). It wasn't like this white lady accused you of rape, and tried to have you killed - which is what happened in The Massie Affair:
http://www.powells.com/cgi-bin/biblio?inkey=62-0670033995-0, or like she was Andrea Yates and you were one of the black (or black looking) guys she falsely accused of taking her kids. Yeah, those are extreme examples, but you get my point-- a clutched purse is bullsh*t when compared to the more serious issues and problems that exist.
Happy writing- hopefully your equivocation on your racial identity is and what it means to you won't shoot you in the foot as your write your statement. And I certainly hope it doesn't hint around the tone of "my mama's black, so give me a hand out"... the adcomm will see right through it. You might, however, be able to play up your diverse background by discussing your multi-ethnic background and how that has infulenced and shaped you as a person, etc etc.
Good luck.