Re: Problem student!!
Sounds like things aren't going so well with the new guy. Did you ever ask him what style of Aikido he did before coming to your dojo? We have someone from Aikikai come to our dojo a year ago, with 12 years under his belt. It took him months to switch over to our way of moving. Younger kyu rank students probably would have a harder time with this- imagine learning 2 years of French and suddenly being switched over to Korean. Also, if he dosen't know how to do a techinique, don't belittle him for it. Beginners are beginners. And yes, beginners (often young, male ones) often crank techinique and then either flop down like a dead fish or never fall at all.
My main concern is why are you so happy about the idea of getting all the sempai to avoid him? Do you think your kohai are magically going to do better with him? As sempai, you should be preventing him from working out with your kohai and working on him. When we get a new belt in our dojo, Sensei says you take on the rank AND responsibility of that rank.
I get it- egotisical people suck. My Sensei has a dojo and a college dojo and I'm in both. And I've watched freshman do the same thing to me and to people who have been practicing longer than I have been alive.
At a year he should be doing better, but just remember- you and everyone in the dojo let this problem go on for that long. And he has been doing this despite being told not to. Don't just blame the kid, blame the parent as well.