As a Los Angeles native who's had the misfortune to live in Boston, I can answer this one: you identify a Boston native by his determination to ignore the rest of humanity. A Boston native is unwilling to make eye contact with anyone he hasn't known for 20 years, unless that eye contact is for the purpose of silently warning others to keep their distance.

(BTW, you identify a Los Angeles native by the smile and wave of greeting to any and all.)