I think you’re confusing gestures. This wasn’t Johnny flipping the bird, which is what he got fined for. This was a totally different signature “Look at Me” move, and he deserved the mocking.
actually manziel was fined by NFL for shooting the bird
http://www.usatoday.com/story/sports/nfl/browns/2014/08/22/johnny-manziel-fined-bird-flip-washington-redskins-cleveland/14440435/