Barnes & Noble isn’t the only thing billionaire investor Bill Ackman wants to take on. He also plans to battle John and Patrick McEnroe in a game of doubles. When the bidding for an hour of tennis with the McEnroes reached $50,000 at the New York Junior Tennis League’s 40th Anniversary Civic Leadership Luncheon the other day, Ackman volunteered that he and rival hedge funder Craig Effron, both avid players, join forces and take the brothers on for a combined donation of $100,000. The league provides free tennis instruction to city schoolchildren.