Being invisible to friends (Suggestion box)

A simple little thing, a button next to away, that makes you invisible to people in your friends list. Sometimes i want to play on my own, or with someone that i can relax with, but at the same time I dont want to offend others by saying no to them and i dont want to be disturbed, I know, a very silly problem, but would be nice to have some sort of stealth mode. They could still invite you if they invited you by inviting you by name.