Visible crew/equipment: When Ted and Dom are looking at Mary, speaking with Warren and Pat from behind the tree, if you look carefully you can see the camera and crew in the reflection in Ted's glasses. (01:10:10)
Visible crew/equipment: When Mary is having lunch with her three friends and she is talking about the kind of guy she wants to meet, you can see the boom mic in the reflection of her sunglasses. (00:30:10)
Visible crew/equipment: When Mary and Ted are driving with the dog on top of the car, when Ted opens the door you can see the camera operator, and the boom mic reflect from the car door. (01:33:50)
Visible crew/equipment: Just before Warren's fishing hook gets stuck in Ted's lip, the camera pans from showing Warren fishing to Ted and Mary. Here you can see the reflection of the crew on the ground and finally on Ted and Mary when they are standing there.
Visible crew/equipment: Ted confronts Tucker and Healy at Healy's apartment. After Tucker says they need a drink and Ted is yelling at Healy, a red object with a black dot appears on Healy's face for an instant.
Answer: Because he is ignorant and doesn't know anything about disabled people, he actually doesn't realise what he is saying is offensive.