“Sell on strength.”
General: The corollary to “buy on weakness.”
When to use it: Any time you don’t actually have the balls to say “sell” but want to be able to say later that you told everyone to sell if the stock goes down.
Why it’s smart-sounding: It sounds highly informed. It sounds prudent (don’t be stupid and sell the stock here, when it’s already down). It will allow you to take credit for predicting any downward move in the stock, while also being able to say “I said sell on strength” if it soars. It hedges all future outcomes, at least over the near term–by implying that the stock will eventually trade higher than it is today, and lower.
Why it’s meaningless: It’s too vague to be interesting or helpful. It can be applied to almost any stock or market at almost any time. It reveals that the speaker has little or no conviction about what he or she is saying–and, instead, just wants to have it both ways.