The feud traces back to 2011 when one of the PG brothers made angry characterizations about hostesses on the PG radio show. The Staff Meal owners found this offensive, so they blacklisted all three PG brothers from being served at Staff Meal food trucks. (See second link in FPP. The original broadcast is no longer available for download on the PG radio show website.)
The food truck vs. brick-and-mortar element began earlier this year when one of the Staff Meal owners wrote an open letter to the City of Boston calling for a change in the structure of Boston's food truck system. The PG radio show picked up the issue in July with a brick-and-mortar restaurant-owner guest who stated that food trucks were hurting his business. (See audio labeled "7/27/12 Al from Al's State Street Cafe.") The next week the Staff Meal owners went on the PG radio show to rebut. (I cannot find the audio on the PG radio website; please post if you can.) Following this appearance, the Staff Meal owners published a blog post titled "Hey Phantom Gourmet" and a tweet showing their "Do Not Serve" poster for the PG brothers.
It is worth noting that Boston magazine handed out the annual prestigious "Best of Boston" awards recently. In the numerous and popular "Food and Restaurant" categories, no awards were given for food trucks.