2a : a holiday celebrated by millions of Mexican nationals in America with notable festivity and drunkenness to commemorate their heritage and pride in the greatness of a country they couldn't wait to leave
2b : a holiday celebrated in Mexico by a small number of Mexicans with overwrought sadness and drunkenness to lament their expulsion from America by the Border Patrol <see also, el día de los muertos>
"Happy Cinco de Mayo! Now go kill some Gringo Bastardos!" Jose Angel Gutierrez
Frat Boy B: Dude: I'm Mexican. That's effed up.
But I'm definitely coming.
"It's good, but we should put some Cinco de Mayo on this bitch."
2) "Yo you wanna go to that Cinco de Mayo party?"
"What? What's THAT?"
"Oh, it's this new thing that they get out of mayonnaise. All the top chefs are using it in their gourmet cooking."
"No wayyyyyy! Yeah, let's go!"