When you were in your 20s and thought about a 49-year-old’s birthday party, what did you think went down?

No matter what you thought, I’m pretty sure you didn’t think the person turning 49 would be rapping in front of a club full of people…right?

Well, that’s how Leonardo DeCaprio rolls!

TMZ bought some cell-footage from one of the people that witnessed this madness at Leo’s 49th b-day party in LA over the weekend. The video is worth every penny TMZ paid, too, because it shows Leo jamming out to Gang Starr and Nice Smooth’s “DWYCK.” And…he’s not bad at all!

In the footage (below) you can clearly see that it IS Leo, but whoever was in charge of how loud Leo’s mic was, they were smart enough to keep it down low…which meant you can just BARELY hear him rapping over the song. Plus, the bonus, he’s not ruining the song for everyone else at the party.

For what it’s worth…Leo seems to know his way around the song the way I’d rock out to Eminem’s “Lose Yourself.”

Happy 49th Leo! Crushin’ it!