Informal:
* Sei pazzo/a! (pronounced "say pat-tso/a") - This is the most common and direct way to say "you are crazy." It is very informal and can be used with friends and family.
* Sei matto/a! (pronounced "say mat-to/a") - This is another informal option, meaning "you are crazy" in a more playful or lighthearted way.
* Sei fuori di testa! (pronounced "say foo-o-ree dee tes-ta") - This translates to "you are out of your head" and implies that someone is acting irrationally.
Formal:
* Lei è pazzo/a. (pronounced "lay eh pat-tso/a") - This is the formal way to say "you are crazy" and is used when addressing someone with respect.
* Lei è fuori di sé. (pronounced "lay eh foo-o-ree dee say") - This is a more formal and neutral way to say "you are crazy" and implies someone is acting unusually.
Other options:
* Hai perso la testa! (pronounced "ahy per-so la tes-ta") - This translates to "you have lost your mind" and is a more dramatic way to say "you are crazy."
* Sei un po' strano/a. (pronounced "say oon po' stran-o/a") - This translates to "you are a little strange" and is a more neutral way to say "you are crazy."
The best way to use these phrases depends on the context and your relationship with the person you are speaking to.