Irish, Mick, (common name among the Irish that became a general epithet for all Irish. Paddy or Pat was also common (and remains so in Britain), but Mick “won out” in the States.
Polish, Polack, simply the older name for Polish people in English (from the Polish word for Pole) that became the pejorative when the word Polish became more prominent.
French, Frog, from the disdain held by “plain eating” English-speaking folk for any group that was so “odd” as to eat frog legs. (I suspect I’m going to get corrected on this one.)
German, Kraut, from the disdain held by “plain eating” folk for people who eat food with rich (or overpowering) odors.
Italian, Wop, from Italian guappo, a street tough–used by association that all Italians were bullies and cutpurses. (Guappo is related to both Spanish guapo and and older French word I’ve forgotten. The French word meant “weak” and the Spanish word means “beautiful” and the word may have originally been an ironic reference among Italian immigrants to the puffed up hooligans in their midst.
Italian, guinea, a linking of Italians to the dark-skinned peoples of Africa, paticularly in the Guinea region.
Hungarian, bohunk, hunky (not honky), from a corruption of the word Hungarian.
U.S. whites (from blacks), honky, purportedly from the higher, nasal sound of white speech as opposed to the lower, throatier sound of black speech.
Dutch, blockhead, or squarehead, I’m not sure of these. Blockhead has meant a stupid person for a long time. It may have simply meant that the English thought the Dutch stupid (when in insult mode) and squarehead may have been a back-formation from blockhead. I’m not sure.
Hispanic in the U.S., spic (also applied to Italians formerly), origin not really understood.
Mexican in the U.S., greaser, an attempt to portray Mexicans as being greasy with grime from never washing.
Jewish, kike, origin also not really understood.
Jew is itself offensive when used as a verb.
Rom, (gypsies), have also incurred a the insult of having their name become a verb meaning “to cheat,” gyp. (Gypsy comes from the notion that the Rom originated (or spent a lot of time in) Egypt. They are actually from the Indian sub-continent.
Korean, (and other East Asian groups by association), slope, an attempt to malign the intelligence of Korean people by indicating that they are “slope-headed” with little fore-brain. (Ironically, most people of the maligned groups have higher foreheads than the European-descended coiners of the term.)
What I have noticed through this list is that there aren’t any names that show any spark or originality. When people want to make a group less than human, they grab fairly mundane ideas (frequently false) and simply slap them on.