Drew Barrymore sets the standard when it comes to tipping ... but not all celebs are as generous.
According to Beauty Undercover, Barrymore -- who dropped an extra $100 for a $200 hair and beauty treatment -- could teach youngins like Paris Hilton, Lindsay Lohan and Britney Spears a lesson.
The site reports Paris, sister Nicky and LiLo often request free hair and beauty services from salons ... and that Lohan "didn't even tip the shampoo and blow dry person."
They also called up the place where Brit infamously buzzed off all her hair -- and while Spears didn't drop a dime, the shop said her bodyguards left a little "something" behind.
Other notable good tippers include Kim Kardashian, Jessica Alba, Nicole Kidman and Renee Zellweger.
