A sudden breaking off in the midst of a sentence, as if from inability or unwillingness to proceed, usually indicating rage or frustration/exasperation. As in "Why I oughta..!" or "One more step and I'll.."
From Late Latin aposiōpēsis, from Greek, aposiōpān, to become silent: apo-, intensive pref.; see apo- + siōpān, to be silent (from siōpē, silence).
Frustrated with the decreasingly funny sentence uses from nerdfury , sea_gaagii wrote a very stern email, filled with exclamation marks and frowny faces. "One more boring sentence, nerdfury," he wrote, "and I'll start threatening with aposiopeses!" Thus demonstrating poor use of aposiopesis.