Gregory Campbell's mockery of the Irish language in the Assembly bordered on racism, the Deputy First Minister has said.
Martin McGuinness heaped pressure on the East Londonderry MLA, who quipped "Curry my yogurt, can coca coalyer".
This was the DUP man's parody of the Irish "Go raibh maith agat, Ceann Comhairle", which means "Thank you, Speaker".
Mr Campbell has yet to apologise for his remarks and insists he has no intention of doing so.
Mr Campbell smiled, laughed and nodded his head as the Deputy First Minister said the conduct had not been befitting for an MLA.
And Mr McGuinness said the DUP man was the only politician out of step with efforts in the Derry area to work for a better future.
He said there were unionists who had a "terrible hatred" not just for the language, but for all things Irish.
"We all have a responsibility to show leadership," he added, and Mr Campbell appeared to mouth the words "on both sides".
Mr Campbell was banned from the chamber for a day last week, although the punishment from acting Speaker Mitchel McLaughlin had little impact because the MLA, who is also an MP, was at Westminster.
Sinn Fein MLA Cathal O hOisin added that politicians should lead by example.