Nail Jell-O to a tree

From Fresh Dictionary

English

Phrasal verb

nail Jell-O to a tree (nails Jell-O to a tree, nailing Jell-O to a tree, nailed Jell-O to a tree)

1. (US slang) To do something that is impossible or very difficult.

   They are asking us to nail Jell-O to a tree if they insist on having everything done in three days.