{ "rules_flag_node_flagged_by_a_user" : {
    "LABEL" : "Flag node flagged by a user",
    "PLUGIN" : "rule",
    "OWNER" : "rules",
    "REQUIRES" : [ "flag", "rules" ],
    "USES VARIABLES" : {
      "flagging_user" : { "label" : "Flagging user", "type" : "user" },
      "flagged_node" : { "label" : "Node to be unflagged", "type" : "node" }
    },
    "DO" : [
      { "flag_flagnode" : {
          "flag" : "your_flag",
          "node" : [ "flagged-node" ],
          "flagging_user" : [ "flagging_user" ],
          "permission_check" : "1"
        }
      },
      { "drupal_message" : { "message" : "Node flagged for user  [flagging-user:name] (uid=[flagging-user:uid])" } }
    ]
  }
}