Common:
* Nar: This is the most common and neutral term for "fool."
* Narish: This is an adjective meaning "foolish" or "silly."
* Shlemiel: This word implies someone clumsy, unlucky, and prone to making mistakes.
* Shlimazl: This word implies someone unlucky and constantly in trouble.
Less Common:
* Narbe: This word is a more informal and playful term for "fool."
* Meshuge: This word implies someone crazy or insane.
The best word to use depends on the context and the nuance you want to convey.