Bottle out
Definition 1 of 1
Pro Tip 1/3Informal Use
Used mainly in casual conversation, not in formal writing or speeches. 
I planned to compete, but I bottled out when I saw the others.
Pro Tip 2/3British Slang
Commonly used in the UK, might not be well-understood by non-British speakers. 
He nearly got the tattoo but bottled out right in the chair.
Pro Tip 3/3Negative Connotation
Implies a lack of courage or commitment, often used to gently tease or criticize. 
They were ready to complain but bottled out when faced with the boss.