I mostly try to go with a friend at least, but I can understand that is not always an option. I tend to block out people completely when I'm not roleplaying with them as some above me stated, I simply filter the background noise as well if that makes sense you know? That said, I do look out for my char's name being mentioned, or something what could refer to them.
Sadly enough I find some people aren't just worth trying to roleplay with; I have a group of people I find absolutely dreadful to roleplay with, they reply, but with just yes or no's, sit there and do nothing to keep the roleplay from evolving naturally, it is really hard to deal with. What I always find a good thing to keep things going is asking questions, most people do tend to respond on that, and if you get a good roleplayer, heck, you will either find plenty of reason to interact in the next line, else eh, just move on, leave the event and try to find other rpers!
Sadly enough I find some people aren't just worth trying to roleplay with; I have a group of people I find absolutely dreadful to roleplay with, they reply, but with just yes or no's, sit there and do nothing to keep the roleplay from evolving naturally, it is really hard to deal with. What I always find a good thing to keep things going is asking questions, most people do tend to respond on that, and if you get a good roleplayer, heck, you will either find plenty of reason to interact in the next line, else eh, just move on, leave the event and try to find other rpers!