To watch your friend while they are wasted out of their mind and don't know what's going on.
"Dude, when you took those 69 hits of acid i had to babysit you for a week. You were out of your mind. I strapped you to the bed to keep you from running out into the street naked and killing the neighbors kids."
The above is a very extreme example of druggy babysitting.
The below is a more average level of babysitting....
When he went into the K-Hole it was up to his friends to babysit him and keep him from swallowing his tounge, vomit, and that he doesn't have snot all over his face.