So, about a month ago, an episode of Community ended with one of the characters telling an anecdote about how he was able to be an extra in Cougar Town. It was pretty forgettable.
And yet, jump forward to the season finale of Courgar Town, (a show I don't watch, but someone on the internet does,) and during a scene with two characters having a conversation at an outdoor table, there in the middle ground… is Abed.
It’s such an extraordinary pay-off to a joke. A joke is set up on one show, and the punchline is in another show, on another channel, in the next month. And as Abed had described it in Community, he panics mid-scene, and runs off the set, catching the attention of the regular characters for a moment. A nice touch.