stand up to someone —(also: stick up to someone) meet an opponent with courage; resist a person:
- If you don’t stand up to this man, he will abuse you unmercifully.
stand up with someone—
1. take part in a dance with a partner:
- I thought you were to stand up with Mr. Tomlinson the two last dances.
2. (also: stand up for someone) act as groomsman or bridesmaid at smb.’s wedding:
- Of course I know John. He stood up with me at my wedding.
Note: Neither expression correlates in meaning with the phrase stand someone up—(coll.) fail to keep an arrangement to meet a person, especially one’s romantic partner:
- Peter said he’d meet me outside the station, but he stood me up.
See also: stand for someone / stand up for someone.