Why can't I use a loop-cut on this simple mesh? I just tried making a person in blender from a tutorial (first time I use blender) and somehow I can't make a loop-cut in the last 'box' thing. 
It is nor a triangle nor an N-gon, I checked for double sides/vertices but nothing seems to work.
How can I get a loop cut here?
The yellow is what blender does, and the red is what I want added
Here's the blend model: http://pasteall.org/blend/index.php?id=50184
You have 2 problems that make Blender unable to know how it could build the edge loop, as it needs quads to create edge loops automatically with ctrl R, and it can't deal with ambiguity:


A face inside your mesh that is not visible in Object mode. You need to select it and delete it with X > Faces
An edge loop coming from the bottom which makes a ngon at its end. You need to select it and delete it with X > Edge Loops


Now you can create a new edge loop.