Last one in is a rotten egg kids
Literal meaning: The last person who jumps into the pool, lake or pond, etc. is rotten egg.
Figurative meaning: Last one in is a rotten egg is often used by children (or by adults with humor) as a way to cheer up others to join in. It especially refers to jumping into water.
“This is where the party is,” said Ed. “Last one in is a rotten egg.”
“C’mon, the water isn’t that bad. Last one in is a rotten egg!”
Act with more effort or enthusiasm
To try to achieve something or succeed in honour of somebody
To motivate someone to do something better, more quickly or more passionately
Used to encourage someone to accept an invitation to somewhere.
This phrase can be related to the idioms good egg and bad egg, as a rotten egg is a very bad egg. However, it doesn't holds that meaning and is simply a way to urge others to have fun.
Used since at least the 1950’s.It may be related to the idioms good egg and bad egg, as a rotten egg is a very bad egg