Let's see now.
1- Not nearly as easy as it sounds. Polyjuice potion is extremely hard to get a hold of, especially for a teenager. Some of the key ingredients are a tad difficult for students to come by, the method is extremely finicky and takes a month, brewing the potion outside of class is banned so because of the time it takes to brew, you'll need a damn good hiding place and finally, if you fuck it up even slightly, well, it's going to end very badly for you. Yeah, let's just say homebrew polyjuice is an absolutely terrible idea. As in, even more dangerous than cheap, dodgy meth level of absolutely terrible idea.
2- The Mirror of Erised, huh? You mean that extremely valuable magical artifact, of which only one exists in the world, was only ever at Hogwarts for a year, during which time it was kept hidden from the students? Yeah, no, that thing would definitely be used by horny teens for a cheap thrill.
3- Yeah, I suppose you have a point there.
4- Assuming you know how to access it sure. However, even Dumbledore didn't know about it until Order of the Phoenix, so it was kind of a secret to all up until that point. Though I will admit that after half the student body used it as a clubhouse for their underground fight club for three years, it's probably safe to assume that it's common knowledge to all from that point onwards.
5- Again, assuming you know that it's not actually haunted and you know the trick for getting past the Whomping Willow, sure. Unfortunately, pretty much nobody knows any of this, and if they did than it would pretty much lose all of its merit as a secret sex dungeon.
6- I suppose that's possible for perhaps an extremely talented 6th or 7th year. Probably not an option for the average horny dullard, though.
7- Sounds great in theory, except it's, well, the prefect's bathroom. Unless you're a prefect yourself, you're probably not getting the password (because what prefect would want everyone else jizzing all over the luxurious indoor swimming pool of a bathroom?) and in either case, there's always the risk of being caught by someone with the authority to issue detentions. Probably not such a grand idea, all things considered.
8- You mean those extremely rare and expensive artifacts that degrade over time (Harry's super cloak notwithstanding)? Yeah, definitely an option for the average teenager looking for a late night quickie.
9- Well, yes. Love potions are indeed very powerful date rape drugs that are for some reason perfectly legal to sell to school kids. That sort of thing is really their sole purpose.
10- Kind of the same problems as polyjuice, only even more difficult to brew and with the added problem that you build up a resistance to it rather quickly (assuming I'm remembering things correctly).
11- That would not work at all. If you were to try going back to the foreplay just to fuck your partner again, well, unless you want to have a threesome with your past self (do doubt there's be someone who doesn't mind), you're in for a rather nasty surprise. Also, I may be misremembering, but don't time turners only work in one hour increments?
12- I suppose that may work. At least this time we finally acknowledge that it's a bit out of reach for teenagers.
13- Again, pensieves are quite rare and very expensive, but no doubt there are some rich people who use them as their own 3D porn cinema.
3/10. Very poor effort, see me after class
