Young celebrity hottie. You're doing things to him/her inside your head that you wouldn't do to a farm animal. Then you remember that they achieved celebrity status when they were just kids. Now, even though they're All Grown Up, you feel like a retroactive pedophile. That guilt you're feeling? AGU-guilt.
You: Gods, Emma Watson...I would love to bend that over and cast Penis Insertium on her!
Friend: Really? Did you feel that way when you saw her in the first Harry Potter movie? Y'know, when she was nine? When did this surge of deviance fall upon you?
You: (silently awash in a wave of AGU-guilt)
Other examples: Alyssa Milano, Kirsten Dunst, Danica McKellar, Lacey Chabert, Hayden Panettiere, etc.