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 but can also refer to a man's shirt if it is a loose-fitting style (e.g. poet shirts and Cossack shirts). 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)