Gintoki's example: Shy school girl becomes slutty after mysterious summer holiday
It is from Episode 136 (season 1), an episode of Hasegawa looking for a 1LDK room.

The scene is about Gintoki giving a nonsense analogy to Hasegawa explaining that a good room has already been "done" by the time you meet, just like girl xD.






To be exact, the scene starts at minute 17:20. Happy rewatching ^^