Knowledge is power.
But when it comes to the professional front a boss will never mind calling you and tell you your weakness. When he tells the same privately one may not feel bad. But if he tells the same in a group or presence of others it may be taken differently.
Whatever may be the way you are trying to convey, it will be good if the other end receives it properly and try to rectify their weakness. Otherwise, all your efforts will be futile only.