One who possesses the ability to clog someone's toilet to the point of OVERFLOW (not merely backup or slow flush) causing shitty water to cover the entire tile floor and parts of the adjacent hallway carpeting. This is not intentional, and happens despite multiple courtesy flushes throughout the act leading to the final shitmastering flush.
Dave: (Running out of the bathroom) Where's your mop bro?
Me: What? Why?
Dave: Your toilet's overflowing man. Shit is literally EVERYWHERE!
Shitfacer is a term derived from the actions of one notably unscrupulous, shitfaced, and lascivious, young man that attends college in Newport Rhode Island. The term has been used as an adjective, noun, verb and in a variety of contexts. The term has been extrapolated to include many other prefixes to the suffix "facer". i.e. Stonefacer, Whorefacer, STDfacer, Spicfacer, "____"facer.
"Hey Pat, can you believe what shitfacer did last weekend?"
That one shit that drops so hard and so fast (almost Matrix style) that before your asshole has a chance to close you get a nice splash of ShitWater back in your hole!