If you are an NFL player, and you have a signature celebration, opposing players will mock it when they do good things against you. EXAMPLE: Every single person who has ever sacked Cam Newton has done the Superman thing.
Johnny Manziel obviously has a signature hand sign -- CASHIN OUT! -- so when he got sacked for the first time in the NFL preseason, obviously somebody on the opposing team did the Johnny Manziel hand sign.
The sack was by Ryan Kerrigan, but it was Brian Orakpo who had the idea to mock Johnny. He's the first, and unless Manziel goes completely unsacked for the remainder of his NFL career, he will not be the last.