Colleen, you're right if this is a regular dojo situation, but as Kevin describes it there is no sensei and often no instructor. This does muddy the waters, and I think this is what Kevin is wanting feedback about.
I don't have enough dojo experience to have an opinion about what to do dojo-wise. But on a personal level, it seems important to honor the informal, club atmosphere when dealing with this guy. By sticking to the social context that exists and remaining friendly and peer-to-peer, it might be easier to get your message across to someone who sounds like he may be acting defensively.
I guess just on a human level, when someone is getting defensive with me, the first thing I do is check myself: Am I being too intense or bossy? Am I not giving the other person an opportunity to be a decent human to me? Coming down to the level on which things are actually happening (rather than the level that things 'should' be happening), being self-deprecating and momentarily siding with the other person - being empathic - often works. Because sometimes I can be too hard to create a real dialogue.
Aikido is hard and frustrating. Maybe it would work to 'blend' with this guy's angst, rather than correct or oppose it?
These are just observations that are taken from my teaching experience - I don't know anything about making this aikido-specific, especially in this freaky club context that I have never really encountered.
There's your advice, along with the big grain of salt. Good luck, sounds like a lame situation.