* If you're talking about Kenny McCormick from South Park: It's actually hard to say who *prevents* people from teasing him. He's a central character in the show and the humor often revolves around him being teased and bullied. However, there are moments where his friends, like Stan, Kyle, and Cartman, stand up for him, albeit in their own often inappropriate ways.
* If you're talking about Kenny from another fictional work: You'll need to provide more context!
Could you please tell me more about the Kenny you're asking about? I'd love to help you figure out who might be standing up for him. 😊