So they accurately portrayed a crazy person by getting Matthew McConaughey to be himself. The next time you go back and watch True Detective, imagine him doing that chest thumping song before every shot. You're welcome!
This explains why the True Detective makeup people put his facial hair on crooked.
Oh, and we should mention that this movie also featured a "not-so-fake punch" incident. In one scene, Hill's character freaks out and lectures his drug dealer, who responds by cold-cocking him. Scorsese wasn't happy with early takes of the scene, so he went to Jonah Hill and asked, "Hey, kid, you wanna try one where he hits you for real?"
Now, keep in mind that the dealer was played by Jon Bernthal, who boxes in his spare time and looks like he works out in a prison yard. Hill, meanwhile, is the quintessential "before" picture from a late night weight loss infomercial. But Hill didn't want to look like a wimp in front of his idol, so he gave in to peer pressure and quite literally took one for the team. The punch was so hard, it sent the fake teeth Hill was wearing flying. It almost looks like he gets knocked out cold, but he's just lucid enough to hear Scorsese's concern as he yelled, "His face is swelling! Get him new teeth and let's shoot it!" Oh, no, he wasn't concerned for Hill's health -- he was worried about missing a good shot.