Do not mess with fish 1

and you thought fish were fun! Attack of the 'willy fish'

Candiru might swim up your penis or vagina if you urinate in the Amazon. The legendary candiru, or 'willy fish' as it sometimes less politely called, is known about well outside its native range in the freshwater rivers of the Amazon basin. These small catfish are parasites and normally live in the gills of very large catfishes, to which they're attracted by the ammonia that is excreted by the fishes' gills. Unfortunately for bathers, gills aren't the only things that can excrete streams of ammonia into water. Humans urinating while swimming also do the same. The tiny catfish home-in on the trickle of ammonia-rich wee and swim up the victim's penis or urethra, locking themselves in place with a set of sharp hooks. Once there, they leave you in immense pain . Although infamous, "attacks" by these fish are actually not thought to be particularly common.

While candiru are normally small fish, given the choice, I think I'd personally prefer to be stung by something instead...