I fully understand GM compels as well as self-compels, they both make sense. However, player vs player compels are still a bit odd to me, so help me understand the concept. If we are assuming that the group of player characters are acting as a team, in which situations would it be suitable? For those that have been playing the game - does it come up often?
I can see it being used by a player wanting help from another player character by compelling his aspect HELPING THE ONES IN NEED, but I have difficulties seeing a player compelling another player like in the example on page YS101.
Errol the Ex-Con Shaman and Reza the White Court Wizard are arguing about the best possible path to rescue Errol's estranged Girlfriend from some White Court Vampires. Rather than engage in the social conflict, Reza decided to compel Errol's aspect of "big brother to the rescue", by telling him that the route Reza wants to take is the quickest route to save his girlfriend. He holds out the fate point from his personal pool, and Errol's player can take it, or pay a fate point to refuse it.
I like player vs player compels because it forces arguments to the question, rather than have them drag out, or force them to beat each other up socially. It creates an opportunity to have friction, but with a reward. It allows a player to back down from another player with a fate point bribe.
One of the player characters in my game, a Sorcerer named "Sweet Johnny", learned most of the aspects of the other players throughout a few sessions (Using Empathy and Rapport skill rolls). As Sweet Johnny learned these aspects, he'd use them to settle arguments, to nudge players characters to do things that benefitted him. It created this manipulative character that was much loved by the other players, because even though characters were getting messed with, it was done with full understanding of the players, who were choosing to be manipulated (they don't have to take the compels).