DespicableCoho is a social experiment bot.
This wiki explains the coho phenomenon. Apparently, it is a social experiment whein two AIM users are randomly linked, and the screenname of each is replaced with the bot’s, so the logs make it look to each person as if the other one is a bot.
My converstation didn’t start with with the opening line the bot usually uses, so either the real user on the other end has a virus bot and coincidentally was skimmed by the fishbot, or the bot has been reprogrammed with different behaviour.