I'm a bit confused. I'm sure I'm way off here, and I apologize in advance, but it sounds as if the only dialogue you've experienced in games are unit chatter in RTS games and some FPS taunts. Way off, right?
Or wait...are you saying that these panelists claim that minor dialogue like chatter and taunts--opposed to major dialogue like character conversations--are a large part of a writer's job in a studio? I really can't imagine that, to be honest. In any case, I don't think you'd need to worry about showcasing any samples of this. If your general dialogue is any good (and obviously represented in your portfolio), any sort of talent for minor dialogue like taunts and one-liners are more or less a given, and I honestly can't see this being a selling point or deal breaker for any prospective employer.
Also, chatter is totally contextual, isn't it? There's really no way to actually sample it without sound really, really cheesy and senseless.