What does "spring stuff" mean?

[Sylphidae]

You don't just spring stuff like that on people.

What does the underlined phrase mean?

[Torsten]

It's a colloquial expression. If you spring stuff on a person you deliver them bad news in a very straightforward and direct way or you ask them a personal or tricky question.

Here is an example:

Starting with last night, I ran upstairs at almost 11 o'clock and ask my half-asleep Dad if I could go to a party and then stay at Martita's. I usually don't spring stuff like that on them but I figured that the worst he could say is no. Well, he didn't. He said yes.
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Test Of English for International Communication
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