// add an event handler to a Pushpin object
var pin = new Microsoft.Maps.Pushpin(<Location> object);
var eventHandlerId = Microsoft.Maps.Events.addHandler(pin, ‘mouseover’, function (event) {
  // some code here to handle mouseover event on pin object
});

// remove an event handler by using the previously created handler id
Microsoft.Maps.Events.removeHandler(eventHandlerId);