How to detect only if back button is pressed?

How can you tell if some pressed the "Go Offline for (person's name)" button on you in the chat room on FB?

• Ok there's this button on fb that if you go in the chat room, you can press the "Go offline for (name of the person)" button. So I guess that means that you can pretend that your offline for someone in the chat room, but your really not offline. So I was wondering how can you tell if someone pressed the "Go offline" button on you? O and if someone in the fb chat room shows their picture on the chat room list and doesn't have a green square next to their name, does that mean their on their phone or did they press the "Go Offline" button on you? Idk if any of this made since, but this is the only way I can explain this. If you don't understand, go on Facebook and press on someone online and then go to tools and then you'll get the option to "Go offline" for them. Please help!

• Answer:

  you simply just cant