Used in several countries of Latin America (previously thought to have originated in Buenos Aires). Also spelled chamullo and the verb infinitive can be chamullar or chamuyar. Among the various shades of meaning, it commonly signifies speaking on a subject with a pretense of authority, when in reality the speaker is simply inventing, or "bullshitting." It can also mean "sweet talk" such as when a guy is "talking trash" to a girl, saying nothing of substance, for the purpose of socializing. Although these uses are largely Spanish and Pocho slang, "chamuyo" appears to be making inroads into English slang.
Don Fulano was using the chamuyo on Josefina for over an hour last night.