1. He keeps his Batman body
When you saw Batman v. Superman, you probably noticed Batman's swole exterior -- there was a whole sequence where he basically did CrossFit -- but what you didn't know is that this is just the new norm for Affleck's shape. Other actors might have slimmed down to play an accountant working out of a strip mall in Plainview, IL. Not Affleck. All his carefully pressed dress shirts look like they're gonna burst off his hulking shoulders, and his many T-shirts will probably inspire elaborate fantasies about Affleck having a Muscle Milk chug-off with Tom Brady on a plane ride to Vegas.
2. He draws math formulas on everything
I love any scene in a movie or TV show where people open boxes, look over spreadsheets, and draw formulas on the walls. Unfortunately, The Accountant is short on actual accounting -- Affleck's character, Christian Wolff, is too busy running from a shady robotics company -- but there is one dynamite scene where Affleck gets to flex his dry-erase marker skills, and it's masterful. Suck it, Will Hunting.
3. He beats his leg with a wooden stick while listening to scary techno
The Accountant is eight movies crammed into one. None of them is very good, but one of them is a very earnest film about autism, like Rain Man with assault rifles. But one of the ways Affleck combats his disorder is by listening to very scary techno and hitting his leg with a big wooden stick while lights flash in his bedroom. Whatever works, man. At least he's not gambling!
4. He befriends his clients
Despite being chilly with his friendly co-workers and living a nomadic existence, Affleck's accounting character does befriend a pair of kindhearted farmers he provides financial assistance to early in the movie. Why does he do this? Because they have a farm where he can shoot things. Great way to keep a low profile and relieve stress.