From an article called "8 insulting ways people act Irish on St. Patrick's day":
#7. Call It "St. Patty's Day"
Every time someone calls it "Patty's" they prove they can't get through 24 hours without thinking of hamburgers. Paddy is short for Padraig (even though the d is silent in some dialects). Pat is short for Patrick, which is an English name. You might be aware of a slight history between the two countries. It still sort of works, but it would be like calling Independence Day "Super Happy Funtime Discount Fireworking Celebration!" You get the idea, but you're still naming one nation's celebration based on the language practices of a different nation with a history of causing your compatriots to be blown up by small, badly made explosives.
So, the question is: is CC racist towards Irish people?