20 years ago I was working in a data center and crossed through an empty rack instead of walking around to the other side. What I didn't notice is that there was something dark mounted at position 35 or so, which blended in with the top of the rack. I hit my head on it and damn near knocked myself out. Had to sit down until the stars cleared from my eyes.

I now have a greenhouse with a narrow aluminum door. Every time I pass through it I look up expecting to hit my head.

Racks in my house? DO NOT WANT. :)