Lets speak about Mentor's.

[Rymm]

First. If you are "grabbing" a Quest you are automatically dismounted.
And when you are reading the dialogue you are facing the NPC. He was looking away from the NPC...
Second: Like I wrote. He was there for a minimum of 3 Minutes
Third: Did you even read what I wrote? I wrote that he was hovering in a way so you could not see the Quest mark. He blocked him.

Wow, 3 whole minutes.

Honestly, it sounds a bit like confirmation bias on your part. Someone parked on a quest giver for a couple of minutes is an inconvenience and yes, a little inconsiderate. But due to your obvious dislike of mentors as soon as you saw the crown you made the jump from something mildly annoying and possibly an unintentional mistake to something maliciously intended and purposefully directed at you and anyone else inconvenienced by it. Given the scanty evidence it's impossible to tell which was the case. Had he not had a crown would you have been more willing to give him the benefit of the doubt? Would you have been more willing to simply let it go rather than letting it gnaw on you like it obviously has been since you are still sore about it?

Some players are jerks. A lot are good people. Some are mentors. Some are not. All of those aspects overlap each other, but none of them constitute the entirety of any other group. Judge people on their behavior, not what symbol they may or may not have next to their name.

Tangentially related, if you hold down X (if you are on PC,) it allows you to click through other players to interact with NPCs or other items in the world. Hope that helps you should a similar situation arise in the future.