Could have been worse, some Jelly's can kill you with one sting, imagine grinding a more venomous jelly into your but crack.. You'd be dead in 5 minutes.
If I had something got in my buttcrack, my first and most important thought'd be "wtf, something is in my buttcrack??!!"
Can you imagine the autopsy report for your own death eternally stating "Cause of Death: Poisonous fish in the ass"? How embarrassing.