No law enforcement is going to go through the trouble of tracking you down and arresting you just because you posted a video of yourself using drugs.
But for the sake of argument, let's say they do track you down and get you in court. How will they prove it wasn't staged? An act? Fake prop drugs?
If you can get convicted for posting a video of yourself doing drugs, then Al Pacino should be in jail for all the "coke" he snorted in Scarface.
Edit: I don't mean to preach, but remember a YouTube video of yourself doing drugs could come to bite you in the ass one day. But then again you could just use the "I was young and stupid" excuse.