Repeat a joke once or twice and it's still funny, but repeat it too much and it just gets annoying. Keep on going, though, and that repetition can make the gag hilarious again, getting a sitcom audience to howl with laughter and feel like they're being greeted by an old friend.
That's exactly why running jokes work so well on television, those little moments and lines that pop up all throughout a series, and the most memorable tend to be the ones that last a ridiculously long time. They're the gags writers stumble upon and then repeat and expand, establishing a sense of continuity to the series. After all, television comedy tends to be pretty episodic, and so this is an effective way to connect the current episode to the show's storied past.
The longer the joke goes, the funnier it often is, just because you can't believe how many damn years the writers have kept it up. Hell, with some of these examples, a kid could be born during the first instance of the gag, and he'd be driving by the last instance.
From slaps to libraries to tripping over steps, here are 10 great running gags that lasted an insanely long time.
10. The Slap Bet - How I Met Your Mother
How I Met Your Mother had an absolutely insane number of running gags throughout the series, including the military salute, jokes about Canada, Barney's job, and Robin Sparkles, but the most prominent one was there for practically the entire damn show.
In the episode Slap Bet from Season 2, Barney loses a "slap bet" against Marshall, a form of betting where the winner can slap the loser once across the face. However, due to a complication, this is extended into five slaps that Marshall can dole out at any time he wishes from then until the end of time. For the next few seasons, Barney always has the threat of a slap hanging over him, a really clever idea which makes it so the writers can surprise viewers with one in any given episode. The most out of nowhere slap happens at the end of Barney's play in Season 2, although usually Marshall makes it into more of a spectacle with Slapsgiving.
The writers loved this gag so much, they actually had to modify the bet to give Marshall more slaps. That way, they could keep the joke going for the full series. It ended up lasting from Season 2 Episode 9 all the way to Season 9 Episode 22, where Marshall uses the final slap at Barney's wedding. Now that's dedication to a bit.