The song was released on Encore.
It’s a diss track aimed at Ray Benzino, the guy who owns The Source, a Hip-Hop magazine. Eminem disses him and says he’s just jealous because he’s not making money like Eminem is and doesn’t even have the rhyming skills Shady has. So he takes it out by talking shit about him.

Eminem mentioned this song in an interview with Rolling Stone in 2011:

Around the tail end of [2004’s] Encore, the songs started getting really goofy. “Rain Man,” “Big Weenie,” “Ass Like That” – that’s when the wheels were coming off. Every day I had a pocketful of pills, and I would just go into the studio and goof off.