Lindsay Lohan‘s not only been a mean girl to Al Gore – she’s been a rude one as well.

The 20-year-old wild-child actress recently blew off a personal invitation to a shindig hosted by the former vice president after promising him she would be there.

The actress met Gore at the GQ Men of the Year awards dinner in Beverly Hills in December and told pals he “would be very happy to have a conversation with me…”

She e-mailed friends that the environmental crusader would help her clean up her image.

But when Lindsay had a chance to reach out to her would-be mentor, she stood him up to party with pals!

She skipped the Dec. 14 “Seeds of Tolerance” event in Hollywood, at which Gore – star of “An Inconvenient Truth” – honored other socially and politically conscious documentary filmmakers.

Now the actress has to deal with her own inconvenient truth. “Lindsay can kiss her friendship with Gore goodbye after snubbing him,” said an insider.

Pick up this week’s issue of The ENQUIRER for all the details!