The opening scene
I actually used to know the actress who appears in the opening scene. She said she only did it to get a SAG card and she said it was kind of low-rent production and that they actually surreptitiously filmed her nude scene (through a one-way mirror or something). I never actually saw the movie until years later, so I never got to ask about the tattoos (it was very unusual for middle-class girls to have tattoos back in the late 80's, and I don't think she would have had a real tattoo that was that lame).
Anyway, I kind of got the impression that whole opening scene was kind of tacked on to pad out the running time (and provide even MORE gratuitous nudity). So that's probably why it doesn't really fit with the rest of the movie.