A colloquial expression in the Southern United States, a person who is "fit to be tied" is angry or livid.
"When he ran over my petunias, why I was fit to be tied!"
I searched high and low for the origin of this idiom that had been such a part of my childhood, but none of my resources had it listed. So I asked my grandma, who said, "They used to tie hogs," as if that were the final word on the matter.
I guess it is for now.
General Wesc says: Various unreliable sources online suggest it's about using a straitjacket on violently mad nutters.