Well..
I'm pretty successful at avoiding these situations.

Basically, all you have to do is rapidly change the subject roughly 5 seconds into the start of the conversation (eg, I have IBS, and i must locate a restroom right now), just try and guess how bad the conversation is by the tone of said persons voice, and make a split second decision and briefly interrupt with a problem of your own which should sound much more serious and urgent.

I got out of one with my dad by using the good old 'I need a shit very badly' excuse.

This only gave me 10 minutes to think about the situation though.

It was about my drunken ramblings the night before.
(Snailfighter Mk VIII MASTER of the bits underneath the ledges on fences, Sat 21 Apr 2007, 21:55, Reply)