Because the thing "I'm really over" is the obsessive re-invention of words. One of these cases is the word "interesting", especially as used among the U.S. upper and upper-middle classes and their imitators for a number of decades now. (Today, in the decline and fall of the West, their discourse regularly functions as a modern court of Versailles, that is, as a slice of hybrid warfare.)
To the larger portion of people, that is, the normal ones (as in the original meaning of the word "normal", i.e. "reflecting the norm"), "interesting" isn't a veiled accusation -- it retains its original meaning, that is, making a statement about the *observer's* emotional reaction (i.e. "I'm entertained to explore this person/thing/whatever further, whatever I find"), and does not involve making insinuations about the target person's character.
It's not a euphemism.
Because the thing "I'm really over" is the obsessive re-invention of words. One of these cases is the word "interesting", especially as used among the U.S. upper and upper-middle classes and their imitators for a number of decades now. (Today, in the decline and fall of the West, their discourse regularly functions as a modern court of Versailles, that is, as a slice of hybrid warfare.)
To the larger portion of people, that is, the normal ones (as in the original meaning of the word "normal", i.e. "reflecting the norm"), "interesting" isn't a veiled accusation -- it retains its original meaning, that is, making a statement about the *observer's* emotional reaction (i.e. "I'm entertained to explore this person/thing/whatever further, whatever I find"), and does not involve making insinuations about the target person's character.