Understand when casualness is appropriate; formal situations usually require a more serious approach. His casualness was welcomed at the barbecue, but not at the business meeting.
Pro Tip 2/3
Connotation
Casualness often implies a comfortable or relaxed attitude, which might be positive or perceived as unprofessional, depending on context. The interviewer appreciated the casualness in her tone, it made the conversation engaging.
Pro Tip 3/3
Not Careless
Casualness does not mean lack of care or effort; it's a relaxed style, not negligence. Despite the casualness of his outfit, he had carefully selected each piece.