I remember Deshaun Jackson doing it when he was with the Eagles, and I thought Andy Reid was going to kill him and cook him right there on the sidelines.
It's one thing if it's some big defensive lineman who recovers a ball, has to run 90 yards, and by the time he gets there he's just totally gassed. I get that- last few yards the other team catches up to you, makes a move for the ball, that I get. Just showboating like what this nimrod was trying to do though? Man, you don't EVER slow down until you've crossed that end zone line. Probably best to slow down after the OTHER side of the end zone just in case. Get the points, THEN act foolish.