The manager of Don Otto’s - a recently shuttered food market in the South End - is blaming neighborhood patrons for its untimely demise, cooking up an angry message to fair-weather fans of the Tremont Street eatery. “Don Otto’s Market wants to say we had few customers that understood customer loyalty and its importance to our business,” a message on its Web site reads, later adding: “If you came in only for baguettes, the occasional piece of cheese, the occasional dinner . . . you can not tell yourself you were a supporter of our market.”