Just because they call it a "friendly" doesn't mean you have to act that way.
Take Barcelona star forward Lionel Messi, for example.
On Wednesday, during one of these so-called matches, Messi can be seen going skull-to-skull with AS Roma's Mapou Yanga-Mbiwa during the 34th minute of the game before delivering a headbutt and then grabbing the larger defender by the throat.
It seems a bit over the line, but Messi and Yanga-Mbiwa only received yellow cards for the incident given the "friendly" nature of the game.
Messi went on to score a goal a few minutes later to give Barca a 2-0 lead before the team's eventual 3-0 defeat of Roma at Barcelona's Camp Nou.
Messi, a four-time Ballon d'Or winner, doesn't typically have to mix it up with opposing players because he's too busy scoring -- in 2014-15 Messi had 63 total goals with Barcelona and the Argentina national team.
He's received exactly one red card during his entire professional career -- and it didn't come in a "friendly."
Follow Matt Wilhalme on Twitter @mattwilhalme