I don't know what to say.
Use this phrase when someone tells you something that surprises you and makes you feel emotional. Some examples of situations in which you can say "I don't know what to say" include:
- someone gives you a very expensive gift which you didn't expect
- you hear that someone's friend or family member has passed away
- your boss tells you that you're losing your job
- someone asks you to marry them, but you're not sure whether you want to