A feeling of unpleasant disagreement and utter irritation, usually evoked in response to someone's outlandish and/or outrageously asinine or naive comments, leaving the aggravated person wanting to tell the speaker to "shut your face", similar to, but not to be mistaken with, the common saying "shut the fuck up".
After Jane Doe turned down John's invitations to each of the first two basketball games, John threatened Jane in a sarcastically and flirtatious tone to not invite her to any more games. In response to this threat Jane said rather directly, "Shfwace! And don't threaten me with no more invites, besides..., it would be hard to find someone as cool as me to invite."
Adjective: characterized by being subjected to a hellacious sequence of unexpected, stressful, unfortunate events leaving a person feeling as they were shitted on.
When she got home from work, Jane Doe went straight to the fridge and poured herself a glass of vino, sat down on her couch, and exhaled with exasperation after having such a shitacious day of dealing with incompetent, complaining coworkers and needy clients.