He might be getting just too friendly in the skies. The CEO of United Airlines was caught flying first class with rival American Airlines, his old employer who he has repeatedly taken jabs at and even pitched a merger to after they let him go a decade ago. Scott Kirby, 58 , was seen on an American Airlines flight from the San Francisco International Airport on Friday, with flight attendant Kristine Tiley snapping a photo with her former boss. United Airlines CEO Scott Kirby took a picture with a flight attendant while traveling first class with rival American Airlines. Kristine Tiley / Facebook “LOOK WHO I HAD IN my first class today from sfo. What a great guy,” Tiley wrote on Facebook . “Just as nice as he was back in the day He misses us lol. And tells everyone Hi.”  The post whipped social media up into a frenzy as many were confused as to why the chief of United Airlines would fly with American rather than with his own company.…