From the University of British Columbia's page on race discrimination and harassment:
http://equity.ubc.ca/discrimination/race-discrimination/
"Racial Harassment
Racial harassment involves unwanted or unwelcome comments, conduct or behaviour that humiliates, intimidates, excludes and isolates an individual or group by focusing on their race, ethnicity, place of origin, or religion. Overall, racial harassment undermines self-esteem and is a violation of the dignity and security of the individual or group(s) that it targets.
Verbal
• Negative or derogatory comments about a racial or ethnic group, their beliefs or religious practices
• Derogatory remarks, insults or slurs about a person’s skin colour or appearance
• Unwelcome remarks about a person’s cultural observances
• Racist jokes and offensive nicknaming or name-calling
• “Universalizing” language and experience which serves to homogenize individual experiences and erase differences between peoples and culture
• Mocking or imitating someone’s accent"
And here are a couple of particularly excellent essays that may give you a better understanding of the impact this sort of racist humor has on its targets, and is equally relevant on issues of gender and homophobia:
http://reverseracism.tumblr.com/post/67909912658/on-asian-accents
https://muslimreverie.wordpress.com/2012/08/24/mocking-foreign-accents-and-the-privilege-of-sounding-white/
http://www.huffingtonpost.com/pp-wong-/funny-ignorant-or-racist_b_4504624.html