In general, yes it unseemly for someone to bring up their ex is "crazy"... unless of course the ex actually is one of those crazy ones will call constantly, or show up in places she knows her ex might be, or stop by his job or whatever. In which case, giving new partners a polite heads up "btw, I have a crazy ex" is not so inappropriate. I don't think we know enough about Brad here to really say what kind of guy he is.
I wouldn't give someone that 'heads up' unless I was going on a date (or more) with them. Talking to someone online...well, that person probably isn't going to feel ramifications of a "crazy" ex at that point. Sure, Brad could be totally right about Claire and maybe Claire will go online and start stalking everyone else he meets. But, if this was the case, Brad has a bigger problem than dealing with a crazy ex. I've never been one to move to a new relationship
when the old one isn't completely tied up and when I was in the dating
world, I had little tolerance for those that did (at least as far as me being willing to pursue something with them.) As soon as a guy mentions an ex right when I meet him
and especially if he starts telling me that she's crazy, my hackles would go up. And maybe I let a couple of good ones go that way, but that was a risk I was willing to take for the very good chance that I was saving myself a lot of drama and heartache by walking away early. But, I digress, as it's not the point of this thread.
The OP passed on some knowledge to Shelly. What Shelly does with that is her business...especially knowing that she hasn't even gone out on a date with Brad yet. And how Brad and Claire handle their relationship
now and in the future is their business. The OP is good to stay out of it.