即堕ち2コマシリーズ 即堕ち2コマ 即落ち2コマシリーズ
Images themed on the "almost comically instant loss" situations. Often used with mating press and chinpo ni wa katenakatta yo.
Pixiv Encyclopedia said that it started as a personal webcomic series by a certain artist. After that, however, the original webcomics were deleted for some reason. The series name is now used as a general tag on pixiv.