How to view someone else's pictures and texts sent on iMessage?

My friend said that he was at our other friends house (on his iMac) when he went through his iMessage and saw a nude pic that his girlfriend sent to him. His girlfriend is an 11/10 and I've always wanted to see her naked. How can I view my friends iMessages on my iPhone 5 discreetly?

You can't unless he sends them to you or you go through his phone.

Take pictures of her on your iPhone 5 while she's showering. Then view the pictures on your iPhone 5.By the way, when you take the pictures, do it discreetly.