Today is a sunny day... but it shouldn't be.
Pinkie is well known for her optimism, parties, and skills in making delicious sweets... she isn't however known for being sad. When she is most ponies keep their distance so as to not make the situation worse by any means. Pinkie doesn't care though. The only one who can make things better now passed away several years ago... but her impact on Pinkie's life remains strong.