Other mistake: After the on-board announcement that the plane is at cruising speed and altitude, the exterior shots still show the wing flaps extended for landing. Due to structural limitations and the extra drag created, the flaps cannot be used at higher speeds.
Other mistake: When Robbie comes back to the house to watch his sister's kids, they start asking him if he's having a nervous breakdown. Watch the kid on the left. Before he repeats what his brother says, you can tell he's about to, but the shot cuts back to Robbie. Then, the kid says his lines as the shot cuts back to him. The editing didn't quite line up.
Answer: "Mile High Club" refers to people/couples that have had sex on an airplane (most commonly in the tiny airplane bathrooms).
LuMaria 1