Wherein I Have Bad Timing

Is there a word for the conception of a joke that, just a little while ago, might've been funny but now just seems kind of lame? I think "postpwnment" could work, though it's inexact. Perhaps if I tell you the joke you can help:

"Knock-knock."

"Who's there?"

"Sarah Palin."

"Sarah Palin who?"

"Exactly."