When does a joke become a ‘dad’ joke?

When it becomes apparent.

What do dentists call their x-rays?

Tooth pics!

"Why does the parrot cost so much?" asks the man. The owner says "Well the parrot knows how to use a computer."

I bought the world’s worst thesaurus yesterday. Not only is it terrible, it’s terrible.

Assistant: So what dimensions do the doors, hinges, walls, and locks need to be so that it all fits?
The person who invented public bathroom stalls: Can't stress how unimportant that part is