Bite one’s tongue signifies stoping oneself (or others) from saying something they really wish to say.
- Actually, I didn’t like the gift but I bit my tongue when she asked.
- Bite your tongue if the party comes up, we can’t spoil the surprise!
Someone who can’t bite their tongue might be told they have a big mouth.
- Have you ever had to bite your tongue during a conversation?
- Have you ever told someone to bite their tongue?