Kim Kardashian just took a wild trip down memory lane -- literally -- recalling a past drug run incident and how, in a way, it ties into her lifelong passion for prison reform.

In the latest episode of "The Kardashians," Kim sat down with a group of incarcerated men during a Sacramento prison visit -- where she recalled the time teen Kim got talked into picking up ecstasy from an apartment ... and thinking back on it has her freaking out, thinking about how it could have gone south.

However, Kim admitted that if she had gotten caught, she knew her attorney dad, Robert Kardashian, would’ve had her back in a heartbeat -- but for the men sitting with her, that kind of safety net never existed.

Kim was joined by Scott Disick, Olivia Pierson, and her sister Kendall Jenner -- the latter who couldn't help but crack up, joking that Kim was having a total "Legally Blonde" moment, pointing out that she spotted an officer basically face-palming at her story!

The SKIMS mogul was chatting with a group of men under 26, all working as wildfire firefighters as part of a program set up by her friend Scott Budnick -- giving them a chance to expunge their records while making a real impact.