Useful phrase to dismiss someone's accomplishment, either because you believe said accomplishment or said someone to be unworthy of praise.

The phrase got widespread popularity when voiced by Chris Rock as part of his routine, "Niggas vs. Black People," a live cut on his 1997 album, Roll with the New on Uni/Dreamworks Records:

You know the worst thing about niggas? Niggas always want some credit for some shit they supposed to do. For some shit they just supposed to do: A nigga will brag about some shit a normal man just does. A nigga will say some shit like, "I take care of my kids."

You're supposed to, you dumb mothafucka. What are you talkin' about? What are you braggin' about? What kind of ignorant shit is that?

"I ain't never been to jail."

What do you want, a cookie?

You're not supposed to go to jail you low expectation having mothafucka.

Source: Rock, Chris. Rock This! New York: Little, Brown & Company, 1998.