Sometimes, when highly paid professional athletes are laid up with an injury, they party hard and work out less. (See Rob Gronkowski, who body slammed one of his buddies at a Las Vegas nightclub last February, landing hard on his broken forearm.) Not so Rajon Rondo, the Celtics All-Star guard who’s close to coming back from a torn ACL. At least judging from his Twitter feed, Rondo isn’t spending his free time clubbing all night. At 10:42 p.m. on Christmas Eve, the 27-year-old point guard posted a picture of graham crackers and peanut butter. “Late night snack,” Rondo wrote.