Fine Gael's newest election candidate for the capital could not name any streets in a Dublin suburb or stations along the proposed Metro line.
Former SDLP leader Mark Durkan also confirmed he will not be moving to Dublin or supporting local sports teams over those from his native Derry.
Taoiseach Leo Varadkar and Tanaiste Simon Coveney were on hand to unveil Mr Durkan as a running mate for former tanaiste Frances Fitzgerald in the upcoming European elections.
Mr Varadkar introduced Mr Durkan by praising his involvement in the Good Friday Agreement and saying he would be a voice for Dublin, the country and the North.
He said Mr Durkan knew the challenges facing Dublin, that he lived here in the early 1980s and has "retained strong links to the city ever since".
Mr Durkan said his selection followed through on a promise by Mr Varadkar that Irish citizens in the North would not be left behind.
He recognised that he was making a "big ask" of the people of Dublin and said he wanted to be honest about his plans to remain living in the North.
He said he would not pretend he was not a Derry person.
He added that he "probably won't become a Dub" and that he would not support Shamrock Rovers over Derry City.
"He will be supporting the Dubs after Derry get knocked out," Mr Varadkar joked.
Mr Durkan quipped back: "Anybody but Tyrone."
Mr Durkan said the people of Dublin are "canny" and "not going to be sold a pup" and they will be right to demand that four MEPs look after their interests.
He was asked if he could name any stations along the controversial proposed MetroLink line and admitted he had not schooled himself on the "ins and outs of the route".
He said he has proved in the past as a minister in the North that he is "quick enough to learn" and he shares the ambition for Dublin to get the Metro it deserves.
Mr Durkan was asked if he could name four streets in the Taoiseach's Dublin West constituency.
Another Northern politician, Austin Currie, was asked a similar question when he ran for a seat there in the 1989 general election. Mr Currie, who was at the press conference, piped up: "I was only asked for three."
Mr Durkan, who was not able to name four streets in Dublin West, said: "I'm making no pretence here. I'm standing on the basis of who I am, not who I'm pretending to be."
He also insisted people in Dublin care about Brexit and "resent" how it has been imposed on the North.
Ms Fitzgerald was asked about the potential impact her resignation as tanaiste - amid the controversy over garda whistleblower Maurice McCabe - would have on voters.
She has since insisted she was vindicated by the Charleton Tribunal, and said: "My record over the years is the lens through which people will judge me, not any particular incident."
Separately, the Cabinet met last night at Farmleigh House for dinner and a briefing on Brexit and other issues.
Ministers were also expected to be prepped by Mr Coveney for the annual St Patrick's Day promotional blitz abroad.