In the toilet, soiled; or hopelessly irretrievable.
Your relationship with Mary went right in the crapper the minute you told her to, "Rub that pie on her hips because that is where it's going to end up anyway".
Thomas Crapper of England is credited for the design and implementation of modern indoor plumbing (including the flushable toilet). Although there is conciderable evidence to the contrary, restrooms/bathrooms are still often referred to as "The Crapper." This word (among others) was introduced to America by their World War I soldiers returning home from Europe.