Following a challenge from Mapou Yanga Mbiwa in a pre-season friendly, it's fair to say Messi blew his top a little.

Barcelona eventually came out as victors over Mbiwa's Roma, but not before Messi decided give the French defender a piece of his mind(forehead). We're assuming the challenge would have to have been fairly full-blooded to make the usually calm Messi throw his head at a player, never mind the throat-grab afterwards. 

Either way, he was lucky to stay on the field.