Unfortunately, the downside of assuming you will know everyone and that they'll be thrilled to see you is the occasional miscue. A couple of weeks ago in Harris Teeter, I approached a woman and bear hugged from behind thinking it was an old friend. Notsomuch. She assured me it was okay and continued with her meat order.
This weekend, I had the lovely pleasure of my old friend and bridesmaid, Georgia Peach, staying with my to celebrate our engagement party. On Sunday morning I met Georgia at a local cafe for Sunday brunch after church and saw her waiting for me in line. I approached slowly, wrapped my arms around her neck, and nuzzled her a bit. When I felt her stiffen, I backed away and realized that the object of my affection wasn't, in fact, my sweet Peach but rather a stranger who looked more than peeved and ready to mace me.
Clearly, there is a time and place for guerilla affection, but that is not, I have discovered, in public places approaching people from behind.