Photobombing is all about perfect timing on the part of the photobomber and the camera perfectly capturing the moment an unwanted visitor entered the shot, so beware those photobombs which are silent but deadly.
These surprise photobombings can cause the sharer quite a bit of embarrassment if they're not careful, so don't get caught by these background buffoons or you'll be hearing about it via social media.
You should carefully scrutinize every photo you take before posting it online, to make sure you don't have anything too personal or racy in the shot and keep people from calling you a boob.
People Who Should Have Checked The Background Of Photos Before Putting Them Online (contains NSFW imagery)