NEW YORK—MTV executive Phillip Blanchard, 42, grounded his 15-year-old son Joshua Monday, after the alternative-rock band Good Charlotte failed to sustain its popularity among viewers of the cable music station. "Joshua needs to learn that his choices have consequences," said Blanchard, who took away his teenage son's credit-card privileges for the week. "Maybe next time, Joshua will think twice before over-hyping some pop-punk crap." As additional punishment, Blanchard had Joshua organize the family's extensive video library of Road Rules episodes chronologically.