Honestly, this kind of "banter" happens all of the time in other sports. The problem is, people take it more personally in tennis, because it is not a team sport(saying The Yankees suck and should die isn't the same thing as saying Federer sucks and should die... the attack on Federer seems more personal). Also, tennis is a "high class" sport(mostly due to the fact it is relatively expensive to play, and has rich historical roots, and is non contact).

People who come from watching sports like American Football, or Soccer sometimes have a hard time fitting in, because "trash talk" is not really accepted in tennis, at any level(even amongst fans).

If you look at, or listen to fans of Soccer, or American Football, they are often very disparaging to the other team, and often disrespectful(and even violent) towards the other team, and their fans. In the end, the VAST majority of these fans are simply engaging in playful banter, and are almost "play-fighting" with the other team, to amuse themselves, and make the game more exciting. Tennis does not have this phenomena, at all, that I've seen(except maybe Brazilians trashing Nadal at the Olympics).

I've participated in both kinds of sports, and enjoy playful banter in Soccer/American Football, but still with Tennis it just doesn't seem appropriate.