No offense, but serious... nut up.
Look, it sucks, I do not like these people because I was in your place once, but seriously. They are making a party and if they choose not to include you than its their decision. One the other hand, I am sorry the tank left because you never have done a speed run before, but it happened, just brush it off.
Do what I did, I am a Sch healer (sometimes WHM if I feel like it) and In the past 4 day I have added and been added to many peoples friends list to heal for them or have them tank for me. I did this by first shouting that I was new LF AK, eventually I got someone to invite me. I then learned and now I have many choices of people without having to do the dungeon finder.
It happens, it is the nature of the world, ya it sucks, but youre not going to change it with a forum post.
<3 Jacorvin