As in reference to the British tank used in WWII, now denotes large females found at parties and other social gatherings (especially involving alcohol) that attempt to get play from unsuspecting males. Often, they are slow and clumsy, and are always extremely bulky. Approach with care.
Hey, check out Jimi over there being attacked by that real Sherman!
The act of doing something mischievous or incoherent while under the influence, intoxicated, or when something is wrong inside of the brain.
Jeff: Dude, I did something so sherman last night, I stole a cop car, took a diarrhea dump in the front seat, and went on the roof of the school and sprayed 'EAT PUSSY' on the top of the building.