We're the Millers

This scene is beyond funny. It's funny because she simply asks him what kind of haircut he would like and he goes on a long comical banter describing what his hair should look like. Using references to Dora the explorer.

Were the millers

They comical element used here was irony. Because he was rambling on about what kind of haircut he wanted and the hair dresser seemed very confused until a man behind him had the exact haircut he was looking for.