I would think it would be easier / more secure to create a table fill it with two columns
dissID | DissText
and then just load it with disses.
then create a math function to select randomly from the table. I imagine this would be a moderator/admin tool (unless this is like the !slap boxing in an irc #chan) so I would (if I could) make a button next to report under posts that triggers reply + auto grabs a diss by triggering that math function and inserting the data from column 2 in that row into the post underneath the quote.
I used to have a few bot scripts some simple some complex...but basically the cool people who were trying to teach made me acknowledge multiple times that hooking into anything outside of the chan/server that the bot is in, is basically making a botnet. I still can't tell you why, I can tell you is that they told me if I manage to do it...it is not their fault...that is the one part I did get at the time.
I will say a bot would be kind of cool, there was an AI chat bot (like this http://www.computerhope.com/zero/) in a room I used to frequent and it would really answer questions and talk back if you acted up. There is a lot of possibilities with IRC but I still think it would be better to use the DB from the forum rather than wait for all the handshaking of an irc server communicating 2 way with your forum.