Does red get you kicked out of the con or something?
If not, this would turn into a game of who can collect the most harassment cards.
If so, then people could simple kick out people they don't like.
Many cons are putting together anti-harassment policies that include sanctions up to and including lifetime bans.
I'm sure some trolls would be excited by the challenge. But I think these will often serve the purpose of letting somebody know that they have very clearly crossed a line and causing to think about their behavior.
