Well, being more serious, City have been pressed at various times this season by Tottenham, Arsenal, Napoli and Liverpool.
Tottenham put Kane, Son and Alli up to prevent Ederson from passing to the back line. Sterling and Sane pushed up during goal kicks, forcing Tottenham's backline to stay with them (can't be offside on a goal kick). That left a huge void in the middle of the pitch that City (especially De Bruyne) exploited to great effect.
Arsenal had some success applying pressure to City's buildup in various games, but they quickly tired. Plus they did it so shitty that City had no issues with passing through the press. There's a video floating around of City passing around the press before releasing on the break to score.
The games against Napoli were more even. I think the results could have gone either way.
I know people laugh at "gegenpressing", but it's a really systematic way of applying pressure at certain areas on the pitch, and at selected times in the game. It's something Klopp has down to a science, and it's why his Dortmund and Liverpool teams were really great against possession dominant teams. Specifically in this game, they didn't force Ederson to goal kick out (and at that point, they're hunting for the second ball), so Ederson passes to Otamendi or Kompany. But they crowd the half-spaces, restricting space in the middle for De Bruyne to spray diagonal passes. He moves wider. This puts more onus on Fernandinho to be the fulcrum for any play. That's what Klopp targets, the link between the center backs, Fernandinho, and City's play makers who are forced wider.
It's really effective, but it takes a lot of training to implement. And it explains why City were so flustered. No one else has pressed them in this manner.
I'm not sure what Guardiola could have done. I would have not started Gundogan. I would have let Sterling play on the wing. I would have started Delph (who has been great in that role all year). Beyond that, it's just execution and ability to play through Liverpool's press, which may involve more focused training sessions on Guardiola's part? Or just hoof it out?