1. A scolding or telling-off.
2. A situation characterized by unnecessarily informal or lackluster clothing.
3. The act of dating someone noticeably less attractive and/or successful than you.
Mrs. Smith gave me a dressing down for being late to the exam.
A tank top at a funeral? Talk about dressing down.
She can do way better than him. I don't know why she's always dressing down.