What exactly is the name of the disease when skinny teenage boys grow boobs?

Male breasts: The term used for the growth of breasts in a male is gynecomastia (gyn-ee-coh-mast-ee-ah) it can be cause by many factors including genetic problems, certain medications and hormone issues. It is basically an enlargement of the breast tissue and can occur in any male regardless of whether they are skinny or fat. This should be seen by a specialist for work up.

Not a disease: Pubertal gynecomastia may effect the majority of males as the begin their pubertal transition. Most are minimal and last 6m to a year, but occasional longer episodes do occur (1-3yr) it is important to separate the true process from fatty breast enlargement that produces a false gynecomastia in overweight kids. Spongy glandular tissue directly under the nipple is absent in the false case.