Thanks to Pulp Fiction, many of its stars have been getting the royale treatment...not to mention some strange reactions. ''It's almost impossible for me to go into a diner,'' says Tim Roth, who tried to rob one in the movie. ''People look at me oddly. Then they send me a free beer to put me in a good mood.'' Costar Eric Stoltz, who played Pulp's sleazy drug dealer, can go one better. While Stoltz was working on a recent episode of Mad About You, a show cameraman brought him a hypodermic needle to autograph. ''I thought this was sort of strange,'' says Stoltz. ''Where do you autograph a hypodermic? Eventually, I signed it on the barrel.''