That time of day when whatever you're doing becomes so irritating that you simply have to cease immediately and exit the area. No matter what the clock states as the actual time, it is still Fuck This Shit O'Clock. Morning, noon and night, any second of any hour can become Fuck This Shit O'Clock. So named because when the moment is reached, people tend to either do a wild, exasperated hand flinging gesture or smash their hands down onto a surface and say "Fuck this shit!!" And then leave.
It should be noted that although the time of Fuck This Shit O'Clock is randomly assigned, some people hate their jobs so intensely that 5pm Monday to Friday becomes Fuck This Shit O'Clock.
"Dave, can you just run me off twenty copies of this on your way past the photocopier?"
"Sorry Sir, no can do. It's Fuck This Shit O'Clock and I'm outta here."