Revertigo is a name Marshall made-up for the phenomenon 'when you're around people from your past, you start behaving like them'. It was introduced in Sandcastles in the Sand when Robin experiences this with her high school boyfriend Simon Tremblay. While Ted neglects the name Marshall made, Lily's old friend Michelle tells that the actual term for this is "associative regression".
- Robin experiences it when she reunites with Simon. In Bedtime Stories, it is hinted that she might have experienced it again when Simon was getting married.
- Lily experiences it when Michelle comes over. While she is unaware of this, everyone else including Michelle herself, clearly see it.
- Ted experiences it with Punchy, which Lily suggests is the only example of it among the gang. Ted briefly experiences again in Glitter, over a phone conversation, which Punchy believes that Ted is "depressed".
There are some more notable examples of this outside this episode:
- In The Yips, Barney experiences the same after meeting Rhonda French, whom he lost his virginity to.
- In Sorry Bro, Ted experiences it again after meeting with his college girlfriend Karen, to which Lily says it's because she is his first love.
- In Hopeless, after reuniting with his father Jerry, Barney again feels like when he was 8 years old and Jerry was "Awesome".