It has been years but once after being delayed all day in JFK on American we were forced to spend the night in SJU. The best option for us turned out to be some who would not lay down seated in the very uncomfortable airport chairs and some who would lay down sleeping on the children's play mats in the kiddie area. It worked, no one said a word to us. We did it because we had no other viable option for the few hours. It was long ago and the rules can change on any given day.

I have also slept on the floor of DIA headed to Aspen. I have never witnessed anyone giving a valid passenger a hard time overnighting in the airport.

For some the worst of it all are the announcements. As the crowds of the day leave the background noise drops. The volume of the announcements that play automatically to watch your bags continue to blare in the silence of the night. I suggest earplugs or good earphone if the person will attempt to sleep.