What do you mean by hitting begonia with pear trees?

This is from the story of two poets Su Shi and Zhang Xian in the Song Dynasty:

When Zhang Xian was 80 years old, she married a beautiful woman of 18 years old. Su Shi and his friends went to visit and asked the doyen if he had any masterpieces. Zhang Xi 'an answered, casually read aloud a way:

I'm eighty and eighteen, and when I was young, I was gray-haired.

It's the same as Qing's upside down, except that there is a flower in the middle.

Su Shi also wrote a poem after listening to it, which was intended to ridicule:

Eighteen brides are eighty lang, with gray hair and red makeup.

Two nights of mandarin duck quilt, pear tree pressing begonia.

It's actually a joke between men. Later, it was used to describe an old man with few wives and Lolita.

Because of the same artistic conception, this film was translated into "a pear blossom a begonia" when it was introduced to Taiwan Province Province.