dress someone down—
1. make smb. wear informal clothes for an occasion:
- Craig was dressed up in a Brioni suit, and what would be the point of that if they were to dress him down for the movie?
2. (coll.) scold or reprimand a person:
- Well, I let Chris have it, dressing him down for his beard! Needless to say, I lost a friend.
dress someone up—
1. dress smb. formally; make a person wear his best clothes:
- Mr. Wilde procured the boy a suit of clothes to dress him up like a gentleman’s son.
2. make smb. wear fancy clothing; disguise a person:
- I dressed her up as a doctor and painstakingly made her rehearse lines for the fancy dress competition at school.