5. Drug Scandal
You only need rumors and possibly pictures for this. Just spread it around that Luke is doing drugs (illegally).
By now you should know how to photoshop or know someone who does and be able to make Luke look like some crazy drug addict. It's best not to do the worst drug you can think of right away if Luke is a fairly healthy looking person.
You can do all sorts of stuff to Luke for this one. There could be a mysterious white powder (icing sugar, flour...) on or with him in a picture along with dark circles around his eyes (sleep deprivation, dark room, photoshop...).