How to Button your Suit
The two main reasons as to why men should adhere to the above mentioned rules are:
1) Sending out a signal that you pay attention to the details
Knowing the rules and wearing it right portray you to be someone “in the know” and setting you apart from the huge number of men out there who violate the rules as they do not wear a suit regularly.
2) Wearing it right makes a suit look better on a man in most situations
A buttoned suit when standing, cuts a cleaner silhouette.
When seated, unbuttoning allows you to sit more comfortably and prevent wrinkles and button stress/popping.
In addition, many 3 button suits are not made to be buttoned on the top (called 2 1/2 suits) and the lower button is almost always in a position where it restricts movement.
Most modern suits have a single-breasted jacket.
Two factors dictate how they should be buttoned: the number of buttons the jacket has and where the buttons are in relation to your waist.
A jacket with a high stance has buttons at and above the natural waist, while a jacket with a low stance (more common these days) has its buttons at and below the waist.
Single-breasted one-button jackets are becoming more common - it is the classic choice for Black Tie events. They should always be buttoned when standing. However, you may unbutton when seated.
The conventional way to button a two-button jacket is to button the top button and leave the lower undone.
However, men who like a very long lapel sometimes button the lower button and fold the lapel all the way down past the top buttonhole.
In addition, an unusually high-stance jacket might look more proportionate when buttoned at the lower button.
Very tall men may need to use the lower button to keep the jacket from spreading out above their waist and exposing the trouser-front and belt buckle.
The conventional method is to always button the middle button and to button the top button if desired, while always leaving the bottom button undone.
You should avoid fastening all three buttons at once as it will make you look stiff.
Double-breasted jackets are almost always worn buttoned and it is very unusual to unbutton one. They are described with the total number of buttons on the suit front followed by the number of working buttons — so a “six-on-four” jacket has six buttons but only four buttonholes.
Generally, you would want to button all the buttons that have working buttonholes. If you plan to leave some buttons undone, it is most traditional to fasten the top button.
However, men who prefer a longer line have been leaving the lowest button undone instead.