Big, bad, and expensive: used to describe a player, often a foreigner, who looks physically imposing and earns a high salary but performs poorly (common in Dominican baseball to describe disappointing imports).
That gringo first baseman is a GMC, he can't hit a thing.
A large, tall, or well-built young man. It can describe a boy who has grown up quickly or a grown man who still acts like a big kid. It is also used as a friendly, informal way to address a guy or a group of people.
Look how big that boy is, he is a muchachon! Good morning muchachones and muchachonas!
A large, bulky, or heavy guy who is often slow or clumsy. (Dominican culture is heavily influenced by baseball, and the term is frequently used to describe heavy-set players who lack speed).
That Motrocolo needs a triple just to score from third.