Running Prop Bet

[youtalkfunny]

[ QUOTE ]
The other day the topic of running comes up, and he eventually bets me that I could not run 5 miles without stopping in 45 minutes (on a regular track)...
...We havn't shook on anything yet, so nothing is set in stone.

[/ QUOTE ]

We haven't shook on anything? What does that mean?

I know what it meant when we were children. It meant, "I'm gonna welsh, because my integrity as a man means absolutely nothing to me."

What does it mean when an adult says it? I've never seen that happen before.