How do you check if you got chest fat or manboobs?

Exam by a Physician: What you are referring to is male breast tissue or gynecomastia. This is more common than most people think and is very common in boys during puberty, resolving on its own in most cases. It is sometimes difficult to tell breast tissue from fatty tissue. Fatty tissue typically feels soft and can be compressed whereas breast tissue is more dense and can feel like a hard lump under the nipple/areola