Comes from the term blitzkrieg used in Nazi Germany during the second world war. Shitzkrieg is when your taking a shit normally a loose watery shit and you fart in mid-shit causing shit particles too spray everywhere making your toilet bowl look like a war zone when you have finished?
Pakreem; jheeeeze maynnn I went to take slash in yo bathroom WTF happened dude I need a gas mask to go piss in there
Fenton; man ate a kebab last night! Woke up with bowels like a lidl bag and took a dump this morning, it was shitzkrieg man shit went everywhere, I feel both mentally and physically drained after that