Men with this kind of body shape are straight from top to bottom with the chest, hips and waist all around the same size. They have slim legs, either thighs and calves. Their B side is the only one point that divides them in two categories: small but round or flat.
This is that kind of body every man aims for, because a well trained rectangle has muscle VS zero fat mass.
When they get fat instead, as I already told for women as well, the first part where your fat goes is the belly.
There are no areas that need minimising so they can get away with most things.
You can wear patterns and decorations both on your top and bottom and still look slim, you can mix-match colors as you prefer; a quick tip is to use light colors for the top piece so your bust will look larger and more muscular.
If you fancy stripes, go for the horizontal ones because the enlarge your chest and balance the entire figure, while vertical stripes would make you appear slimmer, would elongate your bust creating a weird effect and unbalancing the entire figure (nope, if you’re overweight vertical stripes won’t make you look slimmer, I’m sorry)
As for necklines you are free to pick the one you prefer the most (round, V line, collars) as long they’re not too deep.
In case you want to enlarge and make your chest look bigger, try to add bulk with layers, stay in a very close chromatic range and please remember to tuck your shirts in! You can try something like the half tuck or the french tuck for a “sloppy” effect or just completely tuck it in and seal it with a belt. Belts are very useful not only because they prevent you from losing your pants but also because they define a waist line you don’t naturally have. .
Choose light colors and pockets on the chest area for your shirts and jackets. This would make your torso look wider.
Shirt’s collars and the shoulder seam just over your natural shoulder line will help make your shoulder look naturally broader. Remeber to use slim fit shirts with this kind of body shape.
Coats and jackets should have many pockets as possible; leather jackets are better with ornamental zips on your chest too for the same reason I keep repeating, make your torso look larger.
Double breasted jackets and coats are the most favourite because guess what? They make your shoulder look broader.
You can also try coats with a belt on the waist line.
The lenght is not so relevant as you will look good with any leght but I rather want to give you a tip, a rule-ish like “voluminous jacket (as the bomber jacket for example) wants loose trousers”.
Jeans: every kind of waist is fine but don’t get a too low waist jeans or it will give you the appereance you have no waist line at all.
What kind of jeans fit you the best? Regular straight, regular slim, bootcut (they usually have smaller back pockets that make your fanny look rounder), baggy and in some rare case, skinny jeans.
Washed out jeans add more bulk to your thighs.
Bermuda shorts shouldn’t go lower than your knees and must have a straight hem.
Most famous rectangular men are Cillian Murphy, David Beckham, Justin Theroux, Ashton Kutcher, Brad Pitt, Tom Cruise, Ian Somerhalder, Daniel Radcliffe, Jake Gyllenhaal, Jensen Ackles, Chris Hemsworth, Matthew McConaughey.