The Irish singer joined bandmates on Australia's Sunrise this morning, where they were welcomed by thousands of excited fans.
During their appearance, the 'What Makes You Beautiful' group tasted various foods, with Horan trying Vegemite spread for the first time. However, unimpressed with the taste, the 18-year-old spat out the lump of toast.
Writing on Twitter, he told followers: "Can clearly say vegemite is horrible! Like tryin new stuff though."
The broadcaster has now made the remainder of the toast available for fans to bid on, with the money raised going to Australian charity YoungCare.
The eBay listing notes: "The item is perishable and although we will package it so that tampering is evident, we do not advise that it is consumed. We will not be including the mouthful that Niall spat out - because that's just gross."
Opening at $0.99 (£0.64), a succession of bids saw the price rise to $1,000 (£648) within three hours. However, with the price at $15,000 (£9,721), an anonymous user put forward a bid of $50,000 (£32,409).
The individual quickly followed up on his original bid, making separate offers of $80,000 (£50,323), $85,000 (£51,845), $90,000 (£58,326) and $99,999, which was matched by another potential buyer.
It will not be known if the bids, of which 111 have now been placed, are authentic until the auction closes on Saturday, April 14.
Watch the full interview with One Direction below: