Like a Dog with Two Tails

Meaning:
To be tremendously happy.

Example:
When his first child was born, Isaac was like a dog with two tails.

Did you know?
Dogs wag their tails when they’re happy or excited, so imagine how happy a person who is like a dog with two tails would be!

Reference: http://dzspeakingenglish.blogspot.com/2010/04/like-dog-with-two-tails.html