can't believe I'd never heard of this before. I'm just reciting crap I read on memory alpha and a forum post for the most part, but I'll save you a click anyway
back in 1988, some trek fan got a job on the ST:TNG staff and used his knowledge of the lot to break in after hours and attempt to tape an awful and inaccurate tour of the sets. him and his dirtbag friend wander around talking about stealing shit and doing a terrible job of explaining things. I haven't watched much of it with sound (it's over 30 minutes of agony) but I heard enough to tell that the guy is an awful guide, and supposedly most of the shit he says isn't even correct.
it's all so disrespectful. the uniform he's wearing is, ostensibly, stolen from the wardrobe department rather than being homemade, so he's fucking up someone's costume. they wander around picking up fragile props and messing with them, fumbling to figure out how to turn on lights in rooms and furniture (some of which probably would have melted if the lighting was left on for too long) and since they don't really know what they're doing, have no plan, and don't know how to turn on most of the overhead lights (and thank god they didn't or they might have burned down the set) the tour is incredibly disappointing; you can barely see anything. It would almost be a fascinating, one of a kind look behind the scenes, if only there was anything to see.
at one point (around 14 minutes I think) the guy breaks a sickbay biobed. an interview with other staff years later confirms that their production schedule the next day was trashed as a result. this guy is directly responsible for the now-longstanding policy of never hiring fans.
in the end they get chased out by security, and the legend holds that they dropped the camcorder and whoever scooped it up spirited the tape away for however many years before ripping it and uploading it somewhere. The video has been appearing and disappearing on youtube (maybe paramount is getting it pulled, maybe not) but I'm guessing the IA version will last a while.
the guy, claimed to be one Greg Stone, periodically makes sockpuppets on forums (the latest one I saw was from 2011) and tries to get people to discuss the tape, before being ruthlessly insulted and told to fuck off by people who are sick of him trying to milk fifteen minutes of fame out of the One Interesting Thing He Ever Did, Which Caused Material Damage And Lasting Harm.