Trace Adkins (Bones) and Randy McDowell (Hank) became good friends, but when Bones head butts him, it wasn't as much acting as it was real. Randy had a mark on his forehead right afterwards.
The big desk in the tattoo parlor was voluntarily built overnight by the owners specifically for the movie.
Originally the character "Bones" was only going to be seen briefly, just outside the tattoo parlor. But they really liked him, and as the budget grew, they decided to use him a lot more.
In one scene when they're trying to catch the parakeet, it's resting on a branch just outside the diner. It was originally planned that they would try to sneak up on it to catch it. But it unexpectedly flew at Kevin and landed on his shoulder after he dropped to the ground. They had wranglers training the bird, but it was never supposed to do this. In the audio commentary, Kevin Downes said "I had no idea the bird was going to come after me......I'm going down to protect my eye cause I think the bird is coming at my eye". They decided that this was funnier than trying to sneak up on it, so they left it this way.
The hospital where Sean knocks his shoulder back into place wasn't a hospital at all, it was the lobby of the church seen earlier in the film. They were trying to find a real hospital to use, but couldn't seem to find a suitable one. Eventually they had the idea of using the church lobby. It was a wild idea, and they weren't sure if it would work, but they fixed it up to look like a hospital room and it worked well.