When you are drunk/high/vulnerable or other, usually at a party. Another person takes this as an opportunity to take a very unflattering picture of you. sometimes you won't even remember aformentioned picture.
doubly worse when the person posts the picture online
also when you're looking not at your best and you ask your friend not to take a picture and they do anyway. Then you ask them to delete it and they don't but say they will
John: Dude, Kevin posted new pictures on facebook.
Dan: oh cool! from the party?
John: yeah. woooah look at you in this one!
Dan: aww man! i was high as a kite then! He totally picture raped me!
Lucy(sweaty and rough looking after a party): Jenna, don't take my picture i look awful!
Jenna: no worries lucy. I'm just looking at some pictures. *flash goes off
Lucy: hey you lied! You picture raped me! no means no!