The extra "yy" emphasizes the "loca" part, meaning the speaker thinks the person is *really* crazy, possibly in a playful or affectionate way.
Here's a breakdown:
* Tu: You (informal, used with someone you know well)
* es: is
* muy: very
* loca: crazy
Context is key: The exact meaning can vary depending on the context and tone of voice. It could be:
* Playful and affectionate: "You're crazy! (in a good way)."
* Sarcastic: "You're so crazy! (I can't believe you did that)."
* Negative: "You are really crazy."
It's important to consider the situation and the relationship between the speaker and the listener to understand the intended meaning.