The differences between men's and women's T-shirts lies in the physical facets of the design.
T-shirts for women are designed to be shorter than those for men.
Men's T-shirts are usually intended to be fitted around the chest and then flow loosely from there. Women's T-shirts are meant to flatter the curves and are more form-fitting.
Women's T-shirts have cap sleeves whereas men's T-shirt arms are slightly longer.