※Warning: this page's related illustrations may shock you. Get ready before reading on. (Read the summary for details.)
"This is terrible/horrible" is a tag applied to pictures that are, from a commoner's viewpoint, visibly butchered in various ways.
Sometimes it is also applied to images whose content mainly goes either, "they drew an existing character but it's no longer the same" or "there is something about this character that takes it far off the original characteristics", as well as R-18 and R-18G.
Other than that, it is added wherever a bizarre setting or plot development makes the whole thing unfathomable; specifically, it might tell a normally impossible dramatic tale, or have such a theme. There are even cases where the artist him/herself adds the tag.
Oftentimes the tags worrying about the author, like Author is Sick, are used in combo with this.
In the introductory part of Sega Saturn game "Daibouken St. Elmo's no Kiseki", released on 1996-04-19, a villager watches the protagonist's father's destroyed ship and says, "This is terrible"; however, the incentive for this to have become popular and a part of net slang was how well the phrase expressed a player's feelings towards the disparaging second-rate graphics of the game and spread among the players for that sake.
The oldest terrible thing:
What else is terrible:
これはひどい, This is Horrible, Terrible, Cruel, QUALITY
Author is Sick, WTF, I Can See But Hope(希望しか見えない), Chaos, Masterpiece(画伯)
Danger Don't Mix(混ぜるな危険), Mostly Unfitting(だいたいあってない), Mostly Wrong(だいたいまちがってる)