Which word best describes a person who is loud and offensive in their behavior?

The word that best captures a person who is loud and offensive in their behavior is "brash." This term generally describes someone who is overly bold, aggressive, or impudent, often in a way that is shocking or rude. A brash individual tends to disregard social norms, leading to loud and offensive actions that can easily disturb or upset those around them.

In contrast, while "blatant" refers to something that is done openly and unashamedly, it does not inherently describe a person’s behavior as being loud or offensive. "Cantankerous" typically emphasizes a bad-tempered or cranky disposition rather than the loudness or aggressiveness. Meanwhile, "belligerent" denotes an inclination to fight or argue, which can imply a level of aggression but isn't necessarily about being loud or offensive in behavior. Thus, "brash" effectively conveys the idea of someone who is not only loud but also exhibits a disregard for others in their actions.