Final answer:
The item that Johnny described as "a birthday streamer, you pull it and then it just snaps" is called a party popper.
Step-by-step explanation:
The subject of the question is English and the grade level is Middle School. The item that Johnny described as "a birthday streamer, you pull it and then it just snaps" is called a party popper. Party poppers are small devices that contain confetti or streamers and make a loud noise when the string is pulled. Johnny asked David to get something different, indicating that he wanted a different type of party decoration.