Been looking for the movie of this image, or just the scene for a long while. It's my favourite scenario.
http://68.media.tumblr.com/6f99f88467fe36165605aeeedb5395a9/tumblr_oemyq1NFdk1st7pw8o1_400.gif
Bonus if she joins them
http://68.media.tumblr.com/6f99f88467fe36165605aeeedb5395a9/tumblr_oemyq1NFdk1st7pw8o1_400.gif
Sneakily masturbating girl
Watching couple Fuck
Bonus if she joins them