To Chicken Out

Context #1 - 


Tim: Have you heard about the new ride and Magic Mountain called the Death Drop?
John:  Yeah, I heard it's super scary.  Have you been on it?
Tim:  Well, we went there this weekend and I was going to go on it with my friends, but I chickened out at the last minute.
John:  Really?  That must have been a little embarrassing.
Tim:  Yeah, it was!

Context #2 -

Christine: Did you hear about Steve and Carol's anniversary trip to Yosemite?
Stacy:  No, what happened?
Christine:  They agreed to go bungee jumping off this bridge, but Carol was ready to jump and then chickened out.
Stacy: Oh no!  How did Steve take it?
Christine:  He wasn't upset at all.  He actually thought it was kind of funny.

Meaning:  to chicken out is used when someone gets too scared or too afraid to do something so they back out or don't attempt it.