casual (adj)

His casual behaviour was wholly inappropriate for such a formal occasion.
His clothes were artfully arranged to look stylishly casual.
On Fridays, the office has a casual dress code, allowing employees to wear comfortable attire.
The conversation started as a casual chat but soon delved into deeper, more meaningful topics.
They made plans for a casual meetup at the coffee shop to catch up on each other's lives.
The restaurant had a casual atmosphere, making it a great place for friends to relax and enjoy a meal together.