open up on someone—
1. start shooting at a person:
- Just as we reached that spot a group of soldiers opened up on us with rockets, automatic rifles, and grenades.
2. subject a person to a harsh verbal assault or criticism:
- When we’d killed most of a bottle of wine discussing the literary projects, she opened up on me.
open up to someone—
1. (also: open up with someone) talk to smb. frankly or intimately:
- Although he never answered—or perhaps because of it—I opened up to him completely, telling him things I’d never told anyone.
2. become more accepting of a person:
- I stayed during the breaktime, so a few of the boys stayed also. They finally opened up to me especially the quiet ones.