Well, I'm not sure how dynamic queue works, but apparently, if a position is very much sought after and it happens to be your own first pick, then you are most likely to get second pick. Also, supports are rare, and it is natural (but probably not intentional) that players who are willing to be a support, even if only secondarily, are allowed to. I know how you feel, I haven't played as a jungler in ages essentially in Draft and Ranked. That said, I'm not as unlucky as you. So far most people respect the position they've been allocated to and accept their responsibility for it since they chose it as their secondary position. As such I'm not quite sure I sympathise entirely with your frustration even if an ignorant troll came around, since at the end of the day, you are supposed to be able to main at least a champion in at least one lane, so you getting butted off of one position isn't necessarily terrible, as you said.
It is annoying to meet a troll who can't understand that he has to stay put and not mess with the positions, but at the end of the day Riot can't do much. It gave you two positions to choose from, so that you won't have to accept going to a lane that you have no experience in (which was the last system). If some people are just idiots and destroy your experience, a report helps. Dynamic Queue can't be even more augmented, as far as I imagine.
