#2. Harry's Magical Map, and Magical Invasion of Privacy
The Marauder's Map is an enchanted map of Hogwarts, one that shows every inch of the castle and surrounding grounds. If that sounds just like a regular map, the "magical" part is that you can see where everyone is at all times, since all the people on campus are marked with black footprints with their name under them.
It's a hugely valuable object for a young hero who doesn't play by anyone's rules (the main purpose of the map was to let Harry run around on school grounds while avoiding teachers or bad guys). And some of the potential for abuse was mentioned in the movies -- a teacher does angrily ask Harry if he's considered what the villains could do with such a map, since it would tell them where all of the security is.
"Does it need to make a note every time he pops a boner? That seems ... terrible."
But that's just the beginning.
The Horrific Implications:
You already have thought of the invasion of privacy the map entails. It doesn't tell you what the people are doing, but you can pretty much guess. If the two feet are standing with their heels to the toilet, that person is probably taking a dump. There's even an Easter egg at the end of Prisoner of Azkaban where two students are clearly fucking in the corner:
The possessor of the map can see their crush sitting too close to a member of the opposite sex, or they can see their professors sneaking around with each other, feet entangled at the foot of a bed. Then they could just kind of walk in on them for fun, if they were so inclined. Either way, they'd know everything. Now let's give one example where things get really disturbing:
At the beginning of the story, the owners of the map were Fred and George Weasley, the brothers of Harry's best friend, Ron. They had the thing for years, which means that they had to overlook some serious shit, such as their little brother's love affair with a middle-aged man.
This man couldn't look anything more like a pedophile.
In the third book, we discover that an evil wizard named Peter Pettigrew has been in disguise as Ron's rat, Scabbers, for 12 years. We discover this because Harry saw Pettigrew's name show up when he had the map in his possession, despite Pettigrew's disguise as a rodent. So even though Ron thought he was just sleeping with his pet rat, Fred and George saw Ron bedding some guy named Peter every single night.
"That explains why he didn't burrow into my eyes at night."
Oh, and even better: Scabbers was once their older brother Percy's pet until he gave it to Ron. So from Fred and George's perspective, Ron inherited Percy's lover.