5:35 PM PT -- Lamar is coming all the way clean ... he says it was actually a shart.
LO says he suffers from lactose intolerance and IBS ... which did not pair well with his late-night snack of beef jerky sticks, candy and warm milk.
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Lamar's having fun with it all ... he's now calling himself "The Big S******."
No dancing, or even sleeping, around it -- Lamar Odom took a dump in his bed, and he's not ashamed to let his housemates ... and the world know it!!!
The bed pooping incident was caught on the live feeds inside the "Celebrity Big Brother" house early Friday morning, but it's comforting to know Lamar headed straight for the showers to wash his behind after, quite literally, s***ing the bed.
As you can see, Lamar is cleaning up in the shower, and even from the other side of the partition Olympic figure skater Mirai Nagasu notices something is up, and asks if he's really scrubbing as vigorously as it sounds.