The question is in the title.
Without any context, I’m guessing it’s a suit made of fabric with a box / square pattern.
As I recall, a box suit is an untailored suit. Off the rack versus a custom tailored suit. This is from the '60’s, though I think the origin goes back much farther.
Or maybe it is some kind of lawsuit? We need the context!
I think I’d have the same expression if someone dressed me up like that.
That makes sense. I think someone mentioned one in On The Waterfront.
I never heard the term before, but according to several Google Books hits from around 1920-50, a “box jacket” or “box coat” is one that is intended to hang loosely, as opposed to a “fitted” or “semi-fitted” style. The term “box suit” is sometimes used to mean a suit that includes such a garment. Both men’s and women’s garments were described this way.
That also makes sense.
The far more common term for this is “boxy”. If you google “boxy suit” you get a lot of hits for exactly this, describing the cut.
e.g.
When I was a suit-wearing man (in Aus), that was referred to as “American Cut” (as distinct from European cut).
Although as I remember, the really boxy suits were in Singapore and Hong Kong.
I keep expecting to see a link to a picture of David Byrne.
I immediately thought of these monstrosities from the 80’s. A perfectly square jacket that made your shoulders look like they came out from your ears, with fitted pants that made the legs look like a Popsicle stick when you were standing still. In fact, it gave me an earworm of this Fine Young Cannibals video:
I imagined the home-made Halloween robot costumes kids used to make for trick-or-treating.