Exactly what you think it is, a compacted ball of rice used as a projectile.
Dude you missed it at lunch today! Fu Chow Meng got pelted in the face by a Chinese snowball; it wouldn't have been as funny if he didn't enjoy it so much.
when recieving oral sex, and urine escapes the penis, mixing with the semen, creating a yellowish substance in your partners mouth, known as a 'chinese snowball'
Jim: Ey yo cuh. did you fuck her?
John: naw cuh, i gave her a chinese snowball though
Jim: Awe shit man. thats nastyyy!