First thing that comes to mind is the pot smoking professor in Animal House. It was like the second thing I’d seen him in (well, heard, first was that bomb “Final Fantasy”) but I knew he was an actor of some repute, and here he was, in this dinky, undignified role? …Okay!
Alt: A GIF from the movie Animal House. A mustachioed Donald Sutherland kisses Karen Allen on the forehead, and walks back into the kitchen behind her. He opens a cabinet, and reaches upward, causing his white sweater to rise up and expose his naked ass.
I have a recollection, but I can't remember from where, that Donald Sutherland was one of the few reasons Animal House went into production. The studio refused to move forward without an already established star in the cast, so when they said they secured Donald Sutherland, they said “go for it.”
ALT: Animal House Lets Do It GIF