The point of absolute insanity, the loss of all reason and any care about anything and everything. May be reached as a result of extreme anger. Also used to refer to the state the human mind enters when it goes FUBAR under the care of powerful-ass drugs.
"Man, after he pulled that last one on me I was on the verge of fuckshit avenue."
After taking the overdose of LSD, she proceeed to take an hourlong trip down fuckshit avenue.