In Reply to: No flies on you posted by Victoria S Dennis on October 31, 2008 at 15:37:
: : What is the meaning and origin of the saying 'No flies on you'?
: It's a 19th-century slang phrase implying that someone is so brisk and active that no flies have a chance to settle on them. (VSD)
I'd add only that in the 19th century more people lived a rural life, and even if they lived in the city, they saw a lot of horses. Horses and cows ans other ungulates soon become covered with flies when they are standing still, as you are reminded when they flick their tails.