That “dumb” first job taught you how to talk to adults, show up on time and handle a rude customer. Not dumb at all.

The value of a first job has almost nothing to do with the task. Folding, stacking and cleaning teach nothing in themselves, and alongside them you learn to speak to adults who are not your parents, be somewhere at a fixed time for someone else’s benefit, and stay level while a stranger is unpleasant. Those three carry into everything afterward.

Write down what you can do now that you could not in June, because that list is what you will use in an interview later. Then pick one of the three and get better at it this month. Being unbothered by a rude customer is trainable, not a personality.