I think its a stretch to call this a 'feud' since Mac hated pretty much everyone on tour.
But having seen Gilbert play many times, his on court demeanor was among the most irritating of any player I've seen(which makes it funny when he criticizes todays players during his commentary for getting negative etc)
In terms of bad body language and negative comments, Murray has nothing on Gilbert. Gilbert would essentially comment after every point he lost(sometimes loudly) "you should have hit it there!" etc, etc.
Do you see how that would sort of be annoying to an opponent?
and lots of people had issues with Gilbert because of this(not his 'ugly' game, like his book would lead you to believe), he was not popular with other players for the most part.
David Wheaton almost got into a fight with him oncourt. Muster hated him(and said Andre became a ***** after Gilbert became his coach)
And Gilbert doesn't come off well in Andre's book(seemed like he was always trying to get Andre to hate his opponent - like the Becker stuff)
And he wanted Andre to take a walkover over Peter at '94 Lipton instead of postponing the final for an hour so Pete could get treatment. What a nice guy. This new image of the smiling(I never saw him smile when he played) village idiot who seems like one of the guys when he works for espn is nothing like his image when he was on tour.
yelled at gilbert on a changeover "you dont belong on the same court as me!"
There is a long list of players who Mac said that to(or variations of)
I don't think many would remember Gilbert today if he didn't become a coach & write that book(and most of the forum seems to have been born 1985 and later, what could they possibly know about Gilbert as a player)