smartpants

SR is a measure of performance per unit of risk. You should NEVER invest in a stock that has negative shape ratio because the performance of the RFR is superior.

If SR is zero, it means that you are investing in RFR, below zero means that investing in the stock doesn't produce any value since the SR of investing in the RFR is higher.

You can always short a stock with negative expected performance. Hope it's clear.