Stinky Stalker Subdued in Kardashian Kaper

A 20-year-old man was subdued by cops after casing Kris Jenner's Hidden Hills home and coming face-to-face with Kim Kardashian -- and he smelled like hell ... law enforcement sources tell TMZ.

We're told the man drove from Arizona to L.A. at around 4 PM Sunday ... and somehow got past security at the front gate. He made his way to Kris' house and started peering through the windows, when Kim arrived. She became alarmed and called security ... and he fled.

L.A. County Sheriff's deputies were called and found the dude a few blocks away. He told them he was Kendall Jenner's boyfriend and Justin Bieber's stepbrother. That's all she wrote, and he was taken into custody and placed on a 5150 psychiatric hold.

Our law enforcement sources tell us ... he "reeked of body odor."