run off at the mouth
US /rʌn ɔf æt ðə maʊθ/
UK /rʌn ɔf æt ðə maʊθ/

1.
口无遮拦, 滔滔不绝, 胡说八道
to talk too much, especially in a boastful or indiscreet way
:
•
He tends to run off at the mouth when he's had a few drinks.
他喝了几杯酒后就容易口无遮拦。
•
Don't tell him your secrets; he'll just run off at the mouth to everyone.
别告诉他你的秘密;他会口无遮拦地告诉所有人。