"McNigga" can also be used as an exclamation/gibberish when one is excited or can't think of something better to say.
Al taymalikshawn(Mike): McNigga!
Ross(Ben): you goin' to the physics review session?
Al taymalikshawn: McNigga!
Ross(Ben): I'm gon stab youse in the dick nigga!
Dude2: idk McNiggas cant afford anythin else
Dude1: Lets go get big macs