Sydney Sweeney 's Friendsgiving costume was super hot ... and, we mean that literally because she dressed up as Dragon from "Shrek" -- with a sexy twist.

The actress shared a series of photos from her week of hanging out with friends around Thanksgiving ... sharing snaps from a Disney park, a bar and a lake.

One event she and her pals took part in was a party where everyone dressed as their favorite character from "Shrek" ... with Sydney throwing on red horns, a low-cut matching top and bottoms which revealed a lot of her impressive backside like the huge dragon from the hit film series.

She took photos with someone dressed in a giant inflatable Donkey costume ... unclear if this is her man, Scooter Braun -- but, it's fun to imagine it is.

Sydney also took a fun pic with her frie

See Full Page