I've red some definitions of the word "blouse" and not all of them agree. From Wikipedia
A blouse is a loose-fitting upper garment that was formerly worn by
workmen, peasants, artists, women and children.1 It is typically
gathered at the waist (by a waistband or belt) so that it hangs
loosely ("blouses"2) over the wearer's body.1 Today, the word most
commonly refers to a woman's shirt[3] but can also refer to a man's
shirt if it is a loose-fitting style (e.g. poet shirts and Cossack
shirts).[4] Traditionally, the term has been used to refer to a shirt
which blouses out or has an unmistakably feminine appearance.
From the Oxford dictionary
a woman’s upper garment resembling a shirt, typically with a collar,
buttons, and sleeves. 1) loose linen or cotton garment formerly worn by
peasants and manual workers, typically belted at the waist. 2) type of
jacket worn as part of military uniform.
It appears to be technically correct to say a blouse can be a man's article of clothing, but is this accepted in common usage? For example would it be considered offensive (or feminine) to describe a loose t-shirt a man is wearing as a blouse? The following picture is of a man wearing a loose t-shirt but I don't think many would consider it a blouse:
http://supersklep.com/i127980-element-t-shirt-man-machine-sea (image upload not working)
Best Answer
In the US, blouse is regularly used to refer to women's shirts. It is never used to refer to men's civilian clothing. It is sometimes used for men's military uniform shirts, but not T-shirts.