Blisters/zits on genitals...
This was a rescue animal that came in a week after being severely beaten. It turns out that the 'acne' above was from him rubbing against the cage floor, as his rear leg was broken. Once the leg was healed, they disappeared.
Like any animal chins can develop cysts under the skin. Most often they are seen around the jaw area, caused from malocclusion. On the rare ocassion they develop on other parts of the body and are like any normal cyst, where a vet can lance and drain them with the chin suffering no further problems.