Re: Selfish people in the dojo
My teachers always encourage frequent partner changes. And would frequently say something like "pair up-- experienced people pair up with the new students please..." That was sometimes a hint to the experienced folk to help out but also you'll find that sometimes new students will pair up with each other because they feel more comfortable exploring something new with another new student (usually not the best idea).
When I teach I'll make an effort to keep track of how folk are pairing up. If I see too much of what the OP is talking about I'll clap and tell them to change partners and continue practicing. I'll watch the new pair ups and sometimes I'll clap again relatively quickly and say "Okay, experienced pair up with newbs" or "Okay, pair up with someone you haven't trained with yet tonight". So with more regular students of mine I've noticed I rarely have to do that anymore -- I've got them trained and they know that unless otherwise instructed I want them to mix it up.
But all that said... Don't worry about it. When it's time to pair up jet yourself up to someone more experienced and bow. I've seen newcomers stand around once I say pair up waiting for someone to bow to them. Kind of like the shy kid at their first dance. Don't be that kid.
And don't forget this feeling. If you stick around long term remind yourself occasionally to get out there and pair up with the newbs. I do it myself. I'll sometimes hit general practices, bow in to the class and join in. I'll pair up with anyone out there on the floor. I'm not there to teach, but I'm happy to guide a bit and take good ukemi for anyone willing to learn.