One could say 'when will she learn', but who's to blame her when they keep getting younger?
The 50-year-old actress - whose six-year marriage to 34-year-old actor Ashton Kutcher ended a year ago when he ran off with a 23-year-old waitress on the night of his wedding anniversary - is said to be romancing 26-year-old Vito Schnabel, the art dealer son of painter Julian Schnabel.
The pair first got together earlier this month at Naomi Campbell's 50th birthday party for her boyfriend Vladimir Doronin in Jodhpur, India (it was so noisy, the event organiser was arrested), and sources say they couldn't keep their hands off each other. One told the New York Post: "They were dancing and grinding all over each other, openly, in front of other guests." Since the party, the couple have been "quietly spending time together", which is probably for the best.
Vito has a reported predilection for the older lady, having previously dated 49-year-old Elle Macpherson and 35-year-old actress Liv Tyler.
While Ashton has been larking about with new flame Mila Kunis, Demi has been working on her health after being admitted to rehab earlier this year, where she was allegedly treated for eating disorder issues, exhaustion and substance abuse - so she should identify with most 26-year-olds.
Demi and Ashton have yet to finalise their divorce, largely because he's being a stickler over money despite him being the most overpaid person on the face of TV.