You totally came here because of Justin Bieber's tweet.
Anyway, it means Dirty Love and he was refering to Sean Kingston's and Nikki Minaj's song Letting Go (Dutty Love).
The best person you could ever hope for. They care about others more than they do themselves. Though they are looked over time and time again, but they wait in the shadows like a ninja waiting to strike. They also love Chuck Norris.