Blindsiding Prayers

I've noticed lately, something I am completely again when it comes to public prayer, and that is not warning people you are about to start praying. When I was in NYC for Pre-Field Training, I taught a 4th Grade Sunday School with another girl my age. Our 2nd week there (we taught for a total of 4 weeks), a man from the church came in to chat. It was just the 3 of us in the room for about 10 minutes. All of a sudden, he reaches out to shake my hand. I grasp his hand and look him in the eyes, and he closes his eyes and starts praying! No warning! I mean, seriously, I would like some sort of curtesy, "Let's pray." It's not that I don't want to pray with you, it's just that I want to know if we are shaking hands for the purpose of shaking hands or for the purpose of launching into a prayer. Because if I think w'ere just shaking hands, and you just burst into prayer (which gets really awkward for any third parties in the room by the way i.e. my teaching partner), I feel kind of betrayed. This exact same experience with the Hand Shake Prayer occured every week for the remainder of our time as Sunday School teachers.

IT happened again last night. I was having some post-dinner hot chocolate (from Oaxaca!) with the family I rent from. A missionary couple, who are friends of theirs from church, came over to visit as well. I was introduced to the missionaries and we chatted for 5 or 10 minutes about their work with YWAM. The husband missionary, who had been doing most of the talking, finally diverted his gaze from me, because our conversation had come to an end. He leaned back in his chair and randomly said, "Señor," which I assumed meant he was going to address the husband of the house sitting directly beside him. But no. He launches into this prayer out of nowhere. Warning please! IT's weird because in a moment like last night, you actually see everyone but the person praying trying to figure out what's going on. Sometimes you make eye contact, but at the very least, you see people looking around and then a light bulb goes off in each person's head. After a few seconds, everyone's eyes are closed, but you're still reflecting on what just happened. I would love to pray with you, but I'm just gonna need some warning so I don't feel blindsided. I mean seriously, why do people think blindsiding prayers a good idea?