Just buying groceries, thanks
Went to the store tonight on the way home. Typical exchange (some variation on this theme has happened on at least 3 occasions):
Cashier: Donate to xxx disease charity?
MsPhD: Not today, I work on xxx disease, I donate every day.
Bag Assistant: Are you a doctor?
MsPhD: I'm a PhD. I work in a lab.
Bag Assistant (looks me up and down, puzzled expression, sounds doubtful): Oh.