Just say "hi" and you'll be in the running :3 My friends and I have started running roulettes together as a group, and a good chunk of the time we'll have to DF that 4th spot. That person could be guaranteed 3 commendations, but if they say absolutely nothing, they do not get my vote. I require so little to be happy....just give me my "Hello!" dammit. ._.
As someone else said, it's just basic courtesy. We're playing with live people, not NPCs. While I'd love to always be grouped with fun, chatty people, that rarely happens and so I'll settle for a basic greeting.