The original (that is the one the name came from) penis shrapnel story from the Horrifying Things Scale was in fact a Poirot/Hastings epic. But in fact I've read several stories where Watson has erectile dysfunction, it's just that in my experience the injury is left in his leg since that's where it's located in canon. At least I don't think I recall any actual claims of penis shrapnel, but I have been less tolerant of badfic and have been reading much less Holmes/Watson in the last few years.