26.
“Breaking eye contact a little too quickly. I was once at a barbecue with dozens of people. A young, ridiculously beautiful, and recently expecting married couple showed up. They brought their short, squat, funny-man roommate with them. At some point, funny-man and pregnant wife are on opposite sides of the kitchen — I caught a glance between them that was no more than a blink of an eye. But it was the only interaction they had all night. In that instant, I have never been more sure two people were intimate.
“I told my girlfriend, ‘Those two are smashing,’ and she told me to stop being a creep. Six months later, sure enough, everyone found out the roommate and wife were having an affair, and she was carrying his child.”
—u/illepic
Source: https://www.buzzfeed.com/pernellquilon/signs-people-are-having-sex