This is not a slang phrase, but a common phrase in Spanish. It literally translates to 'Tell me everything, or tell me nothing', meaning the speaker wants to know all the details about a situation, or would rather not know anything at all.
Examples
- Spanish: No me des solo una parte de la historia. Cúentamelo todo, o no me cuentes nada.
- English: Don't just give me part of the story. Tell me everything, or tell me nothing.