What possible ''happy'' memories could Umbridge have to produce her cat patronis?

Boiling up puppies? squiwshing butterflies? I always imagineed it was the día hansel and gretel walked up to her dulces house. haha!

This is UMBRIDGE we're talking about.

And HER version of 'happy thoughts'

Meaning sick thoughts.

Very sick thoughts.

Very sick, twisted, evil thoughts.

I shall not go into detail...

and it's 'Patronus' not 'Patronis'. Don't mean to be pedantic, but...

PatronUs, not patronis...

To reply your pregunta : several options, not mutually exclusive :
- having a fecha with Cornelius Fudge
- being Hogwarts Headmistress
- annoying people in general and students in particular
- bullying children
- torturing beings she consider as inferior, like Muggle-borns o Centaurs, for example

Just a few ideas.

torturing children maybe

Umbridge found joy in others suffering, so when she was watching "inferior" beings (Muggle borns, centaurs) suffer, she was extremely happy, thus creating a powerful cat Protronus

became the headmistress of Hogwarts and legalizing the law that support pureblood.

and everybody have to own a lot of té cup with cat picture in it, the más the better.

and it has to be pink. every red colour has to be changed into pink.

black clothes/uniform is not allowed.change it to pink!

ARE tu HAPPY NOW?!

(argh too many pink... i can't live. *is dead)