Odd Language #185: Not That What?

I recently posted the following paragraph on USENET: “For me, a desktop system has much better price/performance than a laptop. As the old joke goes, when evaluating price/performance, be prepared for the occasional division by zero. A laptop is not that bad, but it is not that good.”

The issue: “not that bad” and “not that good” refer to different concepts. “not that bad” is referring to the joke, but “not that good” is referring to the general idea of something failing to be as good as it is thought it should be.