Knicks guard J.R. Smith has already been fined $50,000 by the NBA for attempting to untie opponents' shoelaces, so he has moved on to headbands.
UPDATE: Tuesday, February 25, 4:13 p.m. ET
Smith denies grabbing Carter's headband, despite the video evidence below, per Ian Begley of ESPNNewyork.com:
"No, your eyes were playing tricks on you," he said with a laugh, repeating the refrain a questioner used. "You're reaching for that one. I [already] got fined once for that s---."
--End of Update--
This move seems to be a joke between two friends rather than anything malicious, but considering the person doing it, it's especially entertaining.