Ghost of a flea

Cartoonist H.T. Webster's most famous protagonist was such a wuss, he'd buy a new hat when the one he was wearing got blown onto a patch of ground ground protected by a "Keep Off the Grass" sign. A sign reading "Watch This Space" could render him motionless for hours. He'd rather look at the column holding up the museum's celing, than an abstract statue that the guide book says is of a nude. He was the original Caspar Milquetoast - literally. Caspar Milquetoast was his name, and anybody else who ever used it, got it from him.