Counties are generally joked about way more than individual towns or cities. So I'll talk about some of them instead.
Dublin is "joked about" by the rest of the country, but they can be rather aggressive jokes and there's some genuine hatred there. Similarly Limerick city has an unfair reputation for stabbings.
For more silly examples, Cork is made fun of for being very proud of itself, and people joke that they'll declare independence some day and create "the People's Republic of Cork".
Cavan people have a reputation for being stingy
People in Roscommon probably fuck sheep, or their sisters
Leitrim don't exist
People in Donegal don't know what a train is, or maybe even electricity