Can't rate as an outsider but can post this comment. Very good! Could use a little polish, specifically in these areas:
-Right click to simply drop item like in Source Engine (which I know this is based on, I saw that Cave Johnson reference ;) )
-Keep the physics on the box while you're holding it. If it exceeds a certain distance from where it should be while you're holding it, it should exit your hand, like in Source. Don't worry about physics bugs, they can be incredibly funny which would actually kinda fit the tone you are going for here.
-Glass should be more obvious. Give them scratches or a little less transparency or something.
Now, on to the positives:
-Incredibly clever! A very interesting usage of the theme; feels like I'm an evil saboteur ruining some poor soul's Portal speedrun XD
-Portal reference ;)
-Custom assets are always refreshing. Visual quality wasn't bad either (although some antialiasing would have been nice).
I have a question. What engine did you use to create this game? I've never seen an engine that spits out a pure executable like that except for a decade-old demoscene engine (not even a game engine really).