50buying it
The Traveling Merchant shuffles his stock every visit, so the horn is there for one day and then gone for an unknowable stretch. Buy it the moment you see it or accept that you are waiting.
wearing it
It does nothing. Drop it in a social slot so your real accessory space stays free, and do not carry it to a reforge, since no modifier will attach anything useful to a vanity piece.
the reference
The horn and the line printed on it point at The New Day, the wrestling trio whose entire act was aggressive positivity. The tooltip is their catchphrase with the edges filed off.