But before you start stuffing Prada stock certificates in one of its bank-breaking “bowling’’ handbags, remember that fashion stocks are fickle, subject to the whims of taste and designer temperament. Consider Donna Karan. The stock more or less tanked before the company was bought last year by LVMH. Shares of Ralph Lauren, Guess and Mossimo have also underperformed. Our tip: buy the shoes, skip the stock.