Hmmm... sounds to me like this boss is passive/aggressive and does not like to deal with confrontations or people issues...
If I were the "victim" and the boss came up to me and said "I've been meaning to talk to you about something for a long time, let's make an appointment." I would grab the boss aside at that moment and ask what the issue is and how to best prepare for the meeting. Also, the "victim" should try to be the driver in setting up a specific date and time that is much sooner than three weeks from Friday at 4:00 p.m.... That way, the "victim" has a little bit of control in deferring his or her punishment.

Best of luck. SNA