Sinn Fein MEP Martina Anderson has rejected any kind of border in Ireland after Brexit, telling Theresa May she can "stick it where the sun doesn't shine".
Addressing the European parliament on Monday Ms Anderson said: "Theresa, your notion of a border, hard and soft, stick it where the sun doesn't shine 'cos you're not putting it in Ireland."
The DUP's Sammy Wilson criticised Ms Anderson for her comments. Responding on BBC Talkback, Mr Wilson said: "Martina Anderson was ranting like a fishwife. That was far more offensive than anything Arlene Foster said."
Mr Wilson was referring to the DUP leader comparing Sinn Fein to a crocodile before the recent election.
Ms Anderson was unavailable to respond to Mr Wilson's comments.
On Monday, Sinn Fein's leader in Northern Ireland, Michelle O'Neill, said there was an urgent need for a referendum on Irish unity as the British government had "refused to listen" to the majority of people in the region over Brexit.
Parliament has passed the Brexit Bill, paving the way for the government to trigger Article 50 so the UK can leave the European Union.
Ulster Unionist MP Danny Kinahan said he was concerned that there is no powersharing government at Stormont to negotiate a good Brexit deal.
"As the government embarks on formal negotiations with the European Union it is a sad indictment of the last Northern Ireland Executive that there is currently no Executive in place to feed into the UK negotiating position.
"The final Brexit deal will have significant lasting consequences for our universities, farming and agri-food, the community and voluntary sector, and the business community, amongst others.
"It is crucial that Northern Ireland interests are represented, which I fear is not happening at the moment."