I usually just ignore them or reply "yeah, you're right, I suck at this".

DON'T:
- Get steamed up and start playing badly (this may have been exactly what he wanted you to do)
- Mention Sharkscope, don't let the fish figure out that they're down $3,000 - they might stop playing
- Mention that you were a 72% favourite when the money went in - no need to educate the fish!