Continuity mistake: When Ted enters Healy's apartment and hides behind the door, there is a nearly full bottle of vodka on the table. It is full of caramel-colored liquid. A minute later, when Ted brandishes the bottle to threaten Healy, the bottle is empty.
Continuity mistake: Near the beginning of the film when the time period is 1985, Ted is with his friends and the camera shows Mary biking into school. After the fight Ted offers to walk Mary and Warren home but Mary doesn't have her bike with her.
Continuity mistake: When Mary and her friends are eating lunch, Pat is sitting behind Joanie. There is enough room for someone to walk through. At the end of that scene, when Mary says that she has a vibrator the distance between Pat and Joanie has increased by double if not tripled.
Factual error: When Magda uses her police scanner to listen to Healy's conversations, she explains it just picks up cellular phones, This is incorrect - in the 90s, police scanners picked up conversations on "cordless" landline phones (in a short range), but not cell phones.
Answer: Because he is ignorant and doesn't know anything about disabled people, he actually doesn't realise what he is saying is offensive.