Do We Have This One?. It's that moment where one character tries to convince the other side of their trustworthiness, only to be utterly rejected. Cue the titular comment. Usually occurs to villains after an apparent Heelface Turn but can also be used against the protagonist, sparking his or her determination to prove the opposing party wrong. This line can also be utilized to illustrate the Fantastic Racism prevalent within a society, whether in the real world or within a fictional community of the author's invention.
Hello, Unknown Troper. You'll need to get known to lend a hand here.