Dean calls Sam Sasquatch as he tries to get his drunk brother into bed in the episode 2.11 Playthings. The nickname has become popular in fanfiction to refer to both Sam and Jared.
It is also used by the cast and crew and was apparently a nickname of Kim Manners for Jared. Source
Jensen Ackles' character Alec calls a 6'10" character named Sam "Sasquatch" in episode 2.03 of Dark Angel.