From where does the derisive term for Italians, 'Wop' come from?

American expression from days of Italian immigration to US - they had WOP stamped on their papers meaning 'Without Official Papers'.

Without Official Papers is likely to be an urban legend. It's more likely to come from 'guappo' (ruffian), the Spanish 'guapo' (dandy) or possibly 'vappa' (worthless fellow - one who drinks crap wine).

wop

An epithet used for those of Italian descent. WOP stands for WithOut Papers. Many Italian immigrants had no papers to identify themselves and were branded as WOPs.

NOT!

wop

a racial slur for an Italian or person of Italian heritage. It is often said that this term comes from "With Out Papers" or "Working On Pavement," but it actually comes from the Italian word "guappo", meaning a swaggerer, pimp, or ruffian.

http://www.urbandictionary.com/define.php?term=wop


And then...

Wop
(North America) A racial term for anyone of Italian descent. Contrary to popular belief, it is not an acronym for "With Out Papers", but was derived from an Italian word "guappo", meaning thug.

WOP

NOUN: Offensive Slang Used as a disparaging term for a person of Italian birth or descent.

ETYMOLOGY: Italian dialectal guappo, thug, from Spanish guapo, handsome, dashing, braggart, bully, from French dialectal wape, rogue, from Latin vappa, flat wine, scoundrel.

American Heritage Dictionary

wop

derogatory for "Italian," 1912, Amer.Eng. slang, apparently from southern It. dialect guappo "dandy, dude, stud," a greeting among male Neapolitans, said to be from Sp. guapo "bold, dandy," which is from L. vappa "sour wine," also "worthless fellow;" related to vapidus (see vapid).

http://www.etymonline.com/index.php?search=wop&searchmode=none