Happy December! xD

Friends > Offline

Edit: you will show up as offline but not actually be offline.

Friend list > Select friend > Remove friend.

Block them while you play, unblock them when you sign out.
Really though, if you have friends getting upset at you for enjoying a game, you need real friends.

Tell them to uncheck the "display a notification when my friend joins a game" option in settings. It's their problem, not yours.

Why would they get upset in the first place?

mmmmm F it xP nvm lmao

Why would they be upset that you're playing a different game, but not upset when you refuse to play whatever game they want you to join when you're supposedly not playing any game at all?