A man is showing off what looks like a back tattoo to a blonde woman sitting beside him on a plane. She holds up his green T-shirt; they chat animatedly, leaning in close. If you were seated a few rows away, it might seem like a wholesome interaction; at least they aren’t passive-aggressively jockeying for elbow space! But the woman who recorded and posted the video to TikTok sensed something more sinister: “If this man is your husband flying @United Airlines...