"In "crap school", you could use "crap" as a part of a composite noun, couldn't you?"

Sure. Sort of like English School, or Truck Driving School. Crap school would be a school where one is taught all the fine points of crap. Crap 101 could be taught by a crappy teacher, however, it wouldn't necessarily mean he was crappy because he was teaching about crap; it would just mean that even crappy teachers can get a job teaching crap.

As for nitpicking, silverboy, I only thought I'd join in the inanity and figured, rightfully so, that your response would give me a good laugh. Thanks for that. Moreover, as an "English teacher," you should be thanking me for the correction.