Mean Girls (2004)

A sharp anthropological satire disguised as a teen comedy, this film reunited Lohan with Freaky Friday director Mark Waters and gave the actress her signature role. She plays Cady, a home-schooled naïf who's suddenly thrown into the shark pond of high school social hierarchy, ruled by queen bee Regina (Rachel McAdams, right) and her ''army of skanks,'' the Plastics. Cady manages to infiltrate and sabotage the clique and bring down Regina, only to become a heartless Plastic herself. ''The movie's message is: Be yourself,'' Lohan told EW. ''And be careful what you say, and who you say it to.''