Lola is correct in regards to replying with a NO or No Thanks.the more correct etiquette (if u want to call it that) is to say" I'm (mi) not ready" or "waiting for someone..".Saying as we foreigners normally would No or No thanks-is taken as a slight by some drivers..And Yes, they're plenty of drivers (red or white) that i will not take a ride from-either they're personal attitude and/or the driving habits...No, i just wave my hand and let them go on their way.