You have to wait for it, it's the very last word in this song.

WHEN YOU ARE OLD AND GRAY

words and music by Tom Lehrer
(copy-pasted from https://tomlehrersongs.com/wp-content/uploads/2018/12/when-you-are-old-and-gray.pdf)

Since I still appreciate you,
Let's find love while we may.,
Because I know I'll hate you
When you are old and gray.
So say you love me here and now,
I'll make the most of that.
Say you love and trust me,
For I know you'll disgust me
When you're old and getting fat.

An awful debility,
A lessened utility,
A loss of mobility
Is a strong possibility.
In all probability
I'll lose my virility
And you your fertility
And desirability,
And this liability
Of total sterility
Will lead to hostility
And a sense of futility,
So let's act with agility
While we still have facility,
For we'll soon reach senility
And lose the ability.

Your teeth will start to go, dear,
Your waist will start to spread.
In twenty years or so, dear,
I'll wish that you were dead.
I'll never love you then at all
The way I do today.
So please remember,
When I leave in December,
I told you so in May.