The teenager made the statement as he was greeted by a crowd of supporters at a UK airport.
In an amateur video uploaded on YouTube, the group of fanatics could be seen shouting at Niall as he went through passport control.
When they asked him to stop for pictures the singer continued to walk and asked them: "Remember the last time I walked down here? You shower of ****s."
While many viewers were surprised by the outburst, one fan insisted that 'The X Factor' 2010 contestant wasn’t serious and was simply making an Irish joke.
The comment read: "In Ireland 'shower of ****s' is used as 'a group of annoying people' but in a joking way. You say it all the time it really isn't offensive."
The person who uploaded the footage added: "He's so nice, even though he called us a shower of ****s but hey. It was banter."
The band had returned to Great Britain after finishing their 'Up All Night' tour in the United States.