Will Smith just joined Instagram, and his good pal Justin Timberlake greeted him with a sarcastic welcome via a #ThrowbackThursday post. But it's Smith's savage response that's got the internet talking. "JT -- thanks a lot for the post and the brief education about Instagram, man," Smith said in a video he shared on the platform Friday. "This is my first day, so I'm appreciating the hookup, but, man, I know what #ThrowbackThursday is. I ain't been in a hole."