Hola Inma,
I really like this construction. The words "I'm warning you" or "I'm telling you" are dropped, and I imagine the full meaning would be implied by the tone of voice that the speaker uses.
I wonder whether this is like the reverse of phrases such as "Que tengas un buen día" or "Que disfrutáis el partido" where "I hope / wish" is implied and you are left with "Have a good day / Enjoy the match."??? Perhaps there is a separate lesson on this already, which doesn't come to mind right now.
Saludos
John
