The 27-year-old actress spent 90 days at the Cliffside treatment centre in Malibu, California, on the order of the court and she spent her free time viewing movies she starred in with other patients.
A source told RadarOnline.com: "There was more than once when Lindsay would rent or buy a movie on iTunes that she'd starred in. She basically forced me to watch that crappy movie 'I Know Who Killed Me' with her, the one where she plays a stripper."
'Mean Girls' star Lindsay - who left rehab on July 31 - didn't think there was anything wrong with her seemingly narcissistic viewing habits and was oblivious to the embarrassment experienced by the other patients.
The source added: "She's such an attention seeker that she didn't think it was weird at all to watch her own movies. Everyone else thought it was really embarrassing of her to do that! But whatever. It was like she was trying to re-live a time when she was actually a working actress."
Lindsay - who thanked fans for their support while she was in rehab in a post on her new website - has thrown herself back into work since her substance abuse treatment ended and filmed a cameo for sitcom 'Eastbound & Down' this week.
According to TMZ, the cast and crew were so impressed with her scenes they gave Lindsay a standing ovation when shooting wrapped.
Lindsay - who plays the illegitimate daughter of main character Kenny Powers - was accompanied by a sober coach on set.