The Sleepover

You're at your friend's house about to go out for a lad's night out. While your mate is in the shower, you go and see what his hot sister is up to in her bedroom. You can see right up her robe at her panties while you natter away talking shit to her, but she can see you're getting an erection. She tells you you'd best get rid of that bulge before her brother sees or you'll be in trouble!