Japanese equivalent of saying to keep something to yourself? What's the Japanese equivalent to saying for people to keep something to themselves? Like, "Keep your toilet humour to yourself," or something?

I think you could say it in several different ways:
"keep ... to oneself" []{}[]{}/[]{}/[]{}(/)[]{}[]{}/ etc.

And you could translate it in different ways depending on context, for example:

> * Keep your opinions to yourself. ()
> * Keep your opinions to yourself! ()
> * He often keeps his opinions to himself. ()
> * I'll keep the secret to myself until death. ()
>