Edit in JSFiddle

var A = _.extend({name:'A'}, Backbone.Events);
var B = _.extend({name:'B'}, Backbone.Events);
var C = _.extend({name:'C'}, Backbone.Events);

var whosListeningToMe = function(){console.log(this.name);};

//Have B listen whosListeningToMe event on A and C
B.listenTo(A, 'whosListeningToMe', whosListeningToMe);
B.listenTo(C, 'whosListeningToMe', whosListeningToMe);

//Trigger whosListeningToMe event on A and C
A.trigger('whosListeningToMe'); //logs B
C.trigger('whosListeningToMe'); //logs B

//Have B stop listening to all objects
B.stopListening();

//logs nothing because we told B to stop listening to everything
A.trigger('whosListeningToMe'); 
C.trigger('whosListeningToMe');