Tip (one's) hand informal verb phrase
This idiom refers to allowing someone else to view the cards one is now holding.
To accidentally reveal what you are going to do or what you believe
Keep a secret! If you tip your hand, our plan won't succeed.
I didn't believe in him. Last week, he tipped his hand when having a meeting with the business partner.
Used to tell someone to keep secret what you're about to say
To let a secret out by accident
To be secretly working together
To talk freely and unintentionally disclose private information or secret to others
The verb "tip" should be conjugated according to its tense.
This phrase emphasize that Christmas takes place once a year time, so you should grab this chance to indulge yourself and be good to others.
I've eaten a little more than usual as today is Christmas and Christmas comes but once a year, right?