nonchalantly
adverb
Casually and showing no excitement; coolly unconcernedly.
Examples:
Monika adjusted the tablecloth; as if nothing had happened, she replenished salt in the shaker; and nonchalantly headed for the single chair near the window. Bruno silently moved in the same direction, and Dad immediately sensed impending trouble... (Context: A family dinner is supervised by a social custodian with smelly feet. Children are starting to compete for the only sitting spot near the open window. Source: J∙ Okram - The Mystery of the Rammed Key.)