In the chapter "The Dinner", once the initial cutscene has played out, complete the following tasks:
1) Head to the kitchen, open the recipe book and turn to the final page with the pizza delivery leaflet. When the options appear on screen, select "PIZZA" (by pressing 'X'). Then head to the phone in the lounge area (next to the sofa) and call and order pizza.
2) Head to the bedroom and open the wardrobe (near the bed) and select "Cool" (by pressing 'O') N.B. Dont worry about having a shower even though Jodie will say "Do I have time to shower?" - Select "NO"
3) Finally, head back to the living room and sit down and watch TV by selecting the remote.
Now just wait until Ryan arrives at the front door, play out the rest of the scene naturally and once the chapter has ended, you will receive the trophy "CASUAL GIRL"!