humorous to decide that you are never going to drink alcohol again.
Why are you drinking Coke? Have you signed the pledge or something?
sign the pledge
To take an oath to abstain from drinking alcohol forever. My father was a monster to me and my brothers until he signed the pledge in the late '90s.I noticed Janet drinking 7-Up all night. She either signed the pledge, or she's pregnant.
sign (or take) the pledge
make a solemn undertaking to abstain from alcohol.
sign/take the ˈpledge
(old-fashioned) promise never to drink alcohol: He hasn’t been much fun since he took the pledge.In the nineteenth century there were anti-drinking campaigns, when people were encouraged to sign a promise (= a pledge) never to drink alcohol.