Based on Melani's definitions, the Harlequin is an "other."
Melani defines an "other" as someone who does not belong and is different "in some fundamental way." The other is seen as "inferior" and is treated as such by the group. Unlike an outsider, the other cannot ever hope to belong to the group; the outsider, on the other hand, "has the possibility of being accepted and incorporated."
The Harlequin has no such hope. Tardiness is seen as an act of resistance to a totalitarian society which values order and structure above all else. In fact, members of this society submit to the Ticktockman, who has the ability to turn off their cardioplates (which stops their hearts and causes death) for failing to adhere to the expectations of timeliness. The Harlequin is seen as a disruptive part of society, and the Ticktockman employs the rest of the community to bring an end to the Harlequin's antics. Nevertheless, the Harlequin refuses to comply and instead increases his efforts of mischief.
When the Harlequin is finally caught, the Ticktockman tells him, "You can't adjust. You can't fit in." This is perhaps the most convincing evidence of the Harelquin's place as an "other." The Ticktockman continues, insisting that the Harlequin is a "non-conformist" and demanding that he "live in the world around [him]." The Harlequin refuses, insisting that he would "rather be dead than live in a dumb world."
Some might argue that the Harlequin's character shift at the end is evidence that he can fit in with this society. Yet it is important to note the narrator's explanation of how this happens: the Harlequin "was destroyed." The only way the Ticktockman could force compliance was to completely obliterate the man who existed before, leaving only a shell of the man who used to exist. Therefore, the Harelquin was an "other" who had no hope of being incorporated into society as he naturally existed.