This was not a casual thing, but very well planned.

People are going out in groups now, even on dates, and keeping things casual.

"You may handle me," she said, understanding that this was not a casual thing.

He saw that this was no casual thing with her.

It wasn't at all a casual thing; he expected someone to stop him at any moment.

It would have been a casual thing and not with anyone who was camp, like him.

Giving your oath was not a casual thing to her.

For him this was a casual thing, she thought.

His hate for me is a casual thing now.

Just a casual thing, a couple of dozen people.