From the 14th-Century Urban Dictionary* by way of the Luttrel Psalter:
Vomit Foxes 21 up, 118 down 
To be so surprised/disgusted/annoyed that you spontaneously begin expelling members of the family vulpis from your mouth.
“Oh my, what is that monkey doing with that trumpet? How dreadful. Pardon me, good sir, I must retire to my hereditary family estate and vomit foxes.”
[Related:] hurl beaver testicles signify the incarnation get all reynard on your ass
Or maybe you’ve got a better explanation for this, smart guy:
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*Inspired by the recent quite awesome article at Something Awful.