I only use it for behaviors I really want the model to clamp down on, and I don't think I've ever told the model it was stupid. But I might say something like:

    No, don't f***ing do that! What part of "[previous instruction]" don't you f***ing understand? I am extremely angry and disappointed by your inability to [whatever]. Do better please.

> maybe it could trigger more defensive responses with argumentation to explain its conclusions.

Quite the opposite, it makes the model extremely conciliatory—which in this situation is what I want. If you're hoping to make the model less sycophantic, this is the wrong tool.