Porridge oats, tea, oranges - you're piling the stuff on the conveyor belt when the girl on the checkout reminds you she's a human being by asking:
"Hi, remember me?"
You're faced with a choice. Be honest and say you haven't a clue or wing it. "Oh hello . . . Barbara" - as you name check the badge. "How are you?"
Cousin twice removed? Neighbour's daughter? Sister-in-law . . . No come on, I'm not that bad.
You fish for a couple of clues, and sometimes it indeed turns out to be your half-cousin, neighbour's daughter, sister-in-law, or the woman who persists in delivering an Avon leaflet to your door every month.
More often than not it's one of your former students. Barbara, for now we are friends reunited, rips off my till receipt and offers further clues. "I was in your class for communication," she says. I smile. "I didn't get it though." I turn the smile into a sympathetic grimace. "I left halfway," she says.
Slight feeling of relief - you can't get them through if they're not there, can you? "I'm going to come back though," she threatens as porridge oats, tea, oranges et al are duly stuffed into polythene bags to the tune of "You should . . ." with a chorus of "Why don't you . . ."
You learn to be careful when meeting former students. Short, sharp lesson number one. Bob, a talented and ambitious graduate, was wearing natty corporate overalls and pushing a long line of supermarket trolleys when he dashed across to say a cheery hello. Initial greetings over, I say: "So, what are you doing now?" Puzzled look. "I'm doing this." Get out of that one elegantly.
It's not just supermarkets that prove testing places. You can be in the middle of nowhere walking your dog, when a lone hiker appears, a tiny dot on the horizon who gradually metamorphoses into a young man calling your name. Your dog, more akin to a piece of candy floss on a string than anything approaching canine fierceness, gives a warning growl but he strides joyfully over.
You can write the introductory remarks yourself, as per above. Then he says, several times over: "I only had one talk to do, and I would have completed the whole unit." You get the impression that he expects you to produce a tick sheet from your pocket, and to suggest that there is no time like the present. With a couple of choruses of "you should" and "why don't you", you retreat. "Is nowhere safe?" you ask your dog.
Lest I give the impression that no student I taught ever finished a unit, let me redress the balance and say that this week I also met a former student who is subbing on a local paper, and one who is loving her job in a nursing home, thanks to qualifications completed at college.
Furthermore, the film I saw last night at our arts centre starred two former students, and everybody in the party scene achieved their "perspectives of theatre history" unit.
People say Dundee is a village, where everyone knows everyone else. But perhaps the city is not unique. The "Six Degrees of Separation" project has shown that everyone in the world can be linked through six social ties. The first experiment in 1967 used snail mail, and the most recent used e-mail.
Participants were asked to contact an individual chosen at random, by contacting someone they considered "closer" to the target. In both studies, it took between five and seven contacts to reach the target.
So the next time I face a class of brand new learners, I will remember I am not talking to a class of strangers. With only six degrees of separation, I may well be addressing my neighbour's sister's cousin, the Avon lady's brother's wife or, indeed, my sister-in-law. And whatever the connection, I will do my utmost to get them through because, in Dundee, we're simply bound to meet up again.
Dr Carol Gow lectures in media at Dundee College.