Screw professional courtesy ... "Twilight" author Stephenie Meyer says she won't give E.L. James any casting advice for the upcoming "Fifty Shades of Grey" movie .. because she REFUSES TO READ THE BOOK!!!
Meyer was leaving Hemmingway's in Hollywood with some friends last night when she fired the shot ... and it ain't the first time she's taken aim at the S&M-heavy trilogy.
Earlier this year, Meyer told The Guardian "50 Shades" was "too smutty" for her taste -- explaining, "Erotica is not something I read. I don't even read traditional romance."
It's unclear how E.L. feels about the diss -- but we're guessing she'd probably give Stephenie a pair of those ben wa balls and tell her to go (well, you know) herself.