Kylie Jenner -- Mackin' On Lil Za in Justin Bieber's Weed Kitchen

Kris Jenner won't be happy about this -- her youngest daughter's been hanging out inside Justin Bieber's famously drugged-out house ... and if that wasn't bad enough, she's even getting cozy with his bad news BFF Lil Za ... who was just charged with 3 FELONIES.

The photo was taken Sunday inside Bieber's kitchen -- where the singer's always kept a giant weed stash -- and it's clear ... Kylie is getting comfy with Za.

The other pics were taken earlier this week -- Za posted them on his Instagram ... referring to himself and Kylie as "best friends."

Probably a bad idea -- Za is 20 and Kylie's only 16 ... not to mention the fact that just last Friday, Za was charged with 3 felonies in connection with the police raid on Bieber's house a couple weeks ago.

As we reported, Za was arrested after the raid when police claim they found MDMA (ecstasy) and Oxycodone near him in the house. He's been charged with felony possession of controlled substances and another felony for breaking a jail phone.