So, I was playing on my main, a good aligned character who was not part of any of the criminal guild(I murdered the DB), and Vilkas of the companions gave me a rescue quest, my target was Vipir the Fleet, who was to be rescued from a cave with hungry vampires, I went to the cave, mass murdered me some evil things, rescued him, went to him to RIften, took my leave from him, and because I did a few Thieves Guild quests on another character, I knew his AI would direct him back to the Thieves Guild hideout, the Ragged Flagon. So I decided to follow him, back through the ratways, to the Ragged Flagon inn, then, using with his seemingly unstealable key, he opened the strange door leading to the actual hideout, but the fact that he only unlocked the locked door that was between the actual (unlocked)door leading to the hideout, I could swiftly run past him when he opened the door, and thus run into the hideout.

Due the fact I wasn't part of the Thieves guild, all the Thieves there got mad at me for breaking in and after seconds, they attacked me, forcing me to murder them all but Mercer(who is Essential). Kind of a crazy way to Destroy the Thieves guild without a quest.

Has anyone else tried this or am I the only one(on the forums at least) that done this?

I have never done that.

You got lucky. And good work.

I will try that if I can.