It can pretty much be anything..
The holster for my LCP is a leather belt loop (not a clip) and I thought I had fed my belt through it, of course.
So there I am at the grocery story standing still looking at something on the shelf.
As I habitually do when my pants start dragging down on that side, I give it a nudge up with the edge of my right hand and AH!!.. it pops out and hit the floor... holster and all!
It goes without saying, I scooped it up straight away despite being perplexed by how it happened. Hopefully nobody noticed?
I double check that belt loop thing nowadays