Guys - first date sex is fairly normal but chicks want you to think they aren't sluts. Therefore, they invented the 'knobstacle course'.
It goes something like this:
Girl won't come home with you after dinner, she's not a slut after all. Girl later agrees to come home with you to see your tortoise/paintings/stamp collection whatever. Not that she's a slut or anything. She stays on your sofa until she has 'accidentally' stayed too late. Now it's too late for her to take a taxi home, it's not safe at that time of night. Not that she's a slut or anything. The spare room is prepped. She has no night clothes to wear, you give her a t-shirt that you estimate will barely cover her ass. She changes into that. Not that she's a slut or anything. More TV is watched on the sofa with her head on your shoulder, it's now 2am, you are horny but getting tired. You suggest that you both sleep in the same bed as yours is more comfortable. You tell her we "don't have to do anything" and that clothes will remain on. She agrees. Not that she's a slut or anything. You get into bed, still talking, her head on your chest, a kiss or two but she's not letting it go further. Not that she's a slut or anything. At this point you have lost interest, fuck it, it's 3am, you turn your back to her ready to catch some zzzz's. At this point her hand comes round and grabs your cock. Game on. Not that she's a slut or anything.
Why they do this, I have no idea. I know it's not just me as girls do it to my friends too. If they want a length - why not just give it up as soon as dinner has gone down ? You could both have a good sleep then. Let's face it - as soon as you have them home it's in the bag. Women...