Fecal Fog

A dense accumulation of feces-tainted water vapor trapped in an enclosed area.

This phenomena occurs when someone takes a long hot shower immediately following prodigious defecation.

it can alternatively occur if someone takes a dump while another party is showering.

"I thought she was just showering, and I unknowingly walked into a wall of fecal fog when I opened the bathroom door"

alternatively

"He snuck in and dropped a deuce while I was showering, it kicked up a massive fecal fog that nearly choked us both"