(at around 5 mins) Jaycee and Alice are making out/having sex in the car (a convertible) since Jaycee's mother had told him he couldn't bring her to the house anymore. Immediately after, Jaycee is shown bringing her home in a car which isn't a convertible.
When in the movie Doug writes on the window "I love you", he writes with the finger on the glass that is covered with steam, and it looks nice, but in fact when it's cold and the windows are covered with steam, the steam is always INSIDE the room, not outside.
When Doug meets Eleanor in the airport, Eleanor is wearing her flight attendant uniform skirt backwards. Her kick pleat is in the front. The rest of the flight attendants have their skirts on correctly with the kick pleat in the back.