On the Urban Dictionary website, which aggregates user-generated definitions of slang, one entry defines “Monday” as “Another way of saying [the N-word] without getting caught.” Another person even claims it “originated in Boston,” though other online commenters peg it to the East Coast more generally. Finally, a third definition offers an explanation of “Monday” as an insult, though no hint of why it would be connected to race: “Everybody hates Mondays,” the contributor writes.
This usage of “Monday” began to be recorded on Urban Dictionary in 2006, and it first made an appearance in the online Racial Slur Database two years before that. But it was the popular comedian Russell Peters, a Canadian of Indian descent, who put “Monday” on the map. In a January 2008 standup routine for Def Comedy Jam (widely circulated on YouTube), Peters tells of a Bostonian referring to blacks as “Mondays” and giving the same bigoted clarification that “nobody likes Mondays.” “White people are getting real…clever with their racism,” Peters jokes ruefully."