Along the Chase Bridge level there’s a bathroom off in the way back down a sketchy cement hallway near a loading elevator.
Very easy to hide in for hours I did it last year.
ealry 1990's, my buddy and I left an JGB MSG show via the firestairs (the spot to smoke during hockey or basketball games). About half-way down, there was a door, we open it up and find ourselves in a large room with elephants. At least the circus was in town, it wasn't our headful!!!!
There are def. a bunch of hiding spots at MSG, but weigh the fact there may be harsh penalties to pay under Adolph Dolan's current regime if you are caught!