My boyfriend got so fat he now has man boobs.
Over-exposure to xenoestrogen may give you man boobs.
Gynecomastia is the medical term.
also gynaecomastia, gynecomasty, "condition of a man having breasts like a woman's," 1881, from gyneco- "woman, female" + Latinized form of Greek mazos "breast," variant of mastos (see masto-) + abstract noun ending -ia.
These sites refer to it as:
Here, Gynecoma.com refers to the difference between chest fat and gynecomastia:
Gynecomastia in very simple terms is enlargement of the male chest and is caused by excessive growth of breast tissue or gland. [...] The classification of breast enlargement in men into that which is due to fat and due to breast tissue or gland growth is primarily for the sake of clarity. In reality, things are not that black and white or exactly 100% fat or exactly 100% breast tissue. In the majority of cases of men with breast enlargement, there will always be a combination of fat and breast tissue and this is called mixed gynecomastia. For some, the majority of the mass will be breast tissue and a minority of the mass would be fat or the other way. So in such cases, workouts to lose chest will help to eliminate that part of mass which involves fat.