A state of nervous excitement.
But by and by, sure enough, I catched a glimpse of fire away through the trees. I went for it, cautious and slow. By and by I was close enough to have a look, and there laid a man on the ground. It most give me the fantods. --Mark Twain, Huckleberry Finn
An inexplicable state of irritability or agitation.
"Man, normally I'da been cool with that shit my gal pulled, but damn if I didn't have the fantods somethin' fierce."
"Don't fuck with me today, I've got the fuckin' fantods."
"I put my fist through the wall for no good reason, gotta be the fantods."