I don't even think Hilary Duff ever knew that she was involved in this feud, but yeah, she had beef with Avril Lavigne.
Hilary Duff basically assumed the role of Miss Manners and said Avril Lavigne needed to be nicer to her fans. This is actually true, because have you ever seen the pics of Avril posing backstage with her fans? It's awko taco honey bunches of oats. But then, as a weird form of revenge, Avril decided to clap back at Hilary at the Kid's Choice Awards because that's totally an appropriate place to start shit. She said she wanted Hilary to get slimed because she was talking smack. Well, Avril, you ended up marrying the lead singer of Nickelback, so who really got the last laugh here?