Any person who is remarkable or memorable but for an odd, not necessarily good reason. A person can be a rattler for a variety of reasons including but not limited to height, weight, ugliness, odd clothing, odd speach, loud speach, speaking loudly in a restaurant about private matters as though he/she were addressing the whole place, eyeglasses taped together, body odor or odd odor, speaking to strangers as though running for office, dressing for a funeral in an old t-shirt and blue jeans, singing in a public place for no reason, wearing a funny hat, speaking about oneself in the third person, etc.
Did you see that rattler that just came through the door? He's wearing a red leather suit with gold fringe. He must have come through a time warp!