Have you ever seen some one that you used to know years ago, just out and about in a random place? Do you say hi to that person? Is that being presumptuous? Maybe they don't remember you. Maybe you will make them feel bad if they don't remember your name.
What if that person was in the shipping department for a job you had four years ago? And you saw her every day for a year but not at all since. And you are in Victoria's Secret. And this woman, who once told you about her grandchildren starting junior high, is asking if they have any red mesh thongs in XL. Do you say hi then?
Hypothetically speaking**, of course.
**EEEEEK. Then I saw her at Bartell's and had to restrain myself from yelling, "HI BERNICE! DID YOU FIND YOUR RED MESH THONG?!?!?!?!"