No offense but I spent some time in the DC area in the past few years and have listened to Fred Grandy on his show. Fred Grandy has a good sense of humor and tends to use a lot of self-deprecating humor. I just can't imagine Fred getting uptight about a good joke like that.
It is probably apocryphal. At the time (1989), I was still a clueless liberal working for a Dem congressman. I heard the story from other Dem interns.