Anything related to "The ____ is a lie!" It was funny when Portal did it, not when you repeated it.
"This food smells good!"
"Yeah but how's it taste?"
*facepalm*
"Can I ask you a question?"
"You just did!"
*headdesk*
Memes. All of them. (The possible personal exception being "Kill it with fire")
Also, to directly contrast the people complaining about "That's what she said" jokes, they can be funny with the right timing and when used properly. I particularly like self-depreciating ones. For example:
"Man this is disappointing"
"...That's what she said.

"