Good thread. I probably have a rather unique perspective on this.
My dads side of the family (outside of my late father) are all big Irish fans. My grandpa went to Pittsburgh with my great-grandfather in the 1920s sometime to root for Pitt against ND. During the day, my grandfather (who was 12 at the time) got to meet Coach Rockne before the game and he was "infected" as they say from that moment on as a Irish fan. He was a civil engineer and worked his whole life (while putting 6 kids through school) to be able to acquire ND season tickets. He did that in 1961 and went to every home and away Irish game for 32 years. He was one of those closet recruiters for ND in Western PA and I recall vividly as a little kid being in South Bend for games and sitting/playing in Faust's and Holtz's office. I remember have breakfast with my grandpa and Moose Krause too. My grandpa had a stroke the night of the ND-Stanford game on Oct. 3, 1992 when the Cardinal upset the Irish. He passed in March of 1993 and Holtz came to the funeral. The tickets have been in my family since 1961 and they're in my name now (I also have Pitt season tickets). I cheer for ND every single week EXCEPT when they play Pitt.
One of my greatest memories with dad was when he visited me in Indianapolis and we went to that epic Pitt-ND game where the Panthers won in 4 OT. He wanted to leave at halftime (recall we were out of it 17-3 and didn't really have an answer). Nonetheless, we stayed and I can still see his satisfied face of beating the Irish in South Bend. He was with his dad and saw those great Pitt teams roll over the Irish with TD, et al. Out of military school, my dad was down to choosing to go to Pitt or ND. My grandfather got him into ND but he chose Pitt because he loved the City of Pittsburgh, wanted to be a dentist and also wanted to cut his own path in life. To his last day, some of his closest friends were ones he met while at Pitt--mostly football players. While that was always a cause of some friction between them, he and my grandfather always had a fun little rivalry about Pitt and ND (and they could coalesce around hating the State Penn and Paterno).
I have vivid memories growing up of going to both South Bend and to Pitt Stadium. I was raised to love Pitt, respect college football and respect other fans.
But, I'm a Pitt Panther fan first and foremost and will always Hail to Pitt above all others (even though I'm a subway fan of Pitt).
I strongly dislike the arrogance of some Irish fans because it comes from some sense of entitlement. From my perspective this entitlement and arrogance generally doesn't come from Irish grads. It comes from that pesky and long subway.
Just this weekend at Heinz Field, I was sitting in my seats for the game and I sit next to a nice Pitt fan and his son. I also saw some ND fans that I recognized. All of the sudden in the 2Q, my seat mates, left to get something to eat/drink. These two younger kids (in their early 20s) came and sat in my neighbors seats. I thought (perhaps) that my seatmates traded them tickets or whatever and so I ask these two young guys if they had tickets for these seats. They had ND shirts on but were clearly not ND students. They said no and started to get in my face about it. It took all of my patience to not throw them both over the railing. Nevertheless, I waved to the usher in our section and the kids quickly ran away. The ND fans sitting in front of me thanked me (I could see his ND class ring on his finger). He said, we hate the arrogant side of the subway fans. "Why can't these so called fans, have some respect, respect the opponent and be courteous?" Good question I thought...
As DvY deftly put above, we cannot put fan-bases (particularly NDs) all into a box...Got to just take each at face value and move on. [Maybe we could put all of UPS' in a box though...]
Hail to PITT.