In (one's) glad rags phrase
Wearing one's most fashionable, attractive or formal clothes.
Mary's husband saw her go out in her glad rags, so he asked where she was going.
I'll be in my glad rags at this event tonight—a lot of famous people will be there.
When John came to pick me up for the movie, he was in his glad rags and carrying a dozen roses.
This phrase was formed based on the meaning of the phrase "glad rags", which dates from the late 19th century.
To be hilarious or enjoyable
"He's a serious person.- Yes, not a barrel of laughter exactly".