Which adjective describes behavior marked by disrespectful levity or casualness?

The adjective "flippant" describes behavior that is characterized by a lack of seriousness, especially in situations that may warrant a more respectful or thoughtful demeanor. When someone is described as flippant, it suggests they approach serious matters with a lightheartedness or casualness that can be perceived as disrespectful. This behavior often involves making jokes or dismissive comments when addressing topics that require sensitivity or gravity.

For instance, if a person responds to a serious discussion about a tragic event with jokes or an indifferent attitude, they can be labeled flippant. This term captures the essence of trivializing important issues, which is central to understanding the word's connotation. In contexts where appropriate seriousness is expected, flippant behavior can undermine the gravity of the situation and offend those involved.

The other options lack this specific connotation. For example, "fastidious" relates to being meticulous or attentive to detail; "grievous" refers to something very serious or severe, and "hackneyed" means something that is overused and lacking originality. Since these terms do not embody the idea of disrespectful levity, they do not fit the description as accurately as "flippant."