Lionel Messi headbutts Roma defender in friendly that wasn't so friendly

Lionel Messi very rarely shows emotion. The biggest outpouring of feelings from Messi has come after painful defeats in international cup finals where he can't hide his utter disgust in failing to carry Argentina to a championship (see: 2014 World Cup, 2015 Copa America).

In a sport where gesticulation often isn't enough to let the world know that you just scored, to the point where special messages are sometimes written on undershirts to completely express one's joy, Messi maintains a much reserved on-pitch persona.

[FC Yahoo: Watch Cristiano Ronaldo show off his skills in full disguise]

That's why it was so shocking to see Messi express so much anger in Barcelona's preseason friendly against Roma on Wednesday. Not only did the diminutive Argentine headbutt Roma's Mapou Yanga-Mbiwa but he also gripped his left hand around the defender's neck and pushed him away as an exclamation point to his seething protest.

Referee Javier Estrada Fernandez watched the altercation unfold right before him but chose to only punish them with yellow cards. Twitter was abuzz with reaction to The Messi Headbutt Seen Around the World, most of it rationalizing that Messi didn't get sent off because he's, well, Lionel Messi. Some pointed to the new tattoo that covers Messi's right arm as the reason, as if a newly tatted Leo is suddenly someone you shouldn't mess with. Oh, Twitter, you cease to amuse and entertain.

In a related story, Barcelona beat Roma 3-0 at the Camp Nou in the traditional Gamper Trophy preseason match.