I’m adopting a new policy and I invite all other veg*n bloggers to join in:

A comment from a user isn’t worthy of a thoughtful response if they use the “plants feel pain” argument (this goes double if it’s already been discussed in the comment thread. The way I figure it, anyone who brings out this unbelievably tired and limp argument isn’t serious about having any real discussion, so I’m refusing to waste time on them.

I think this goes for real life situations, too.