You have the legal right & ability to move freely in society without being harassed or threatened by harm but you must also use common sense & good judgement.
You can not start a argument or scream at someone then as they move to attack you, draw a firearm & shoot them.
If you have a dispute you should be a mature adult & leave w/o incident(as suggested by sworn LE officer/legal use of force expert; Massad Ayoob) or contact LE/private security or guard(if there is a security guard available).
You can use lethal force if you are attacked & in fear for your life but I can honestly tell you, your location, dress, actions, demeanor, background(criminal history), and other factors may be involved in a use of force incident.
The recent Martin/Zimmerman mess is a good example.
It's not fair or ethical but it's the real world in 2013.
ClydeFrog