This is a bit hard to answer, I kinda categorise happiness a lot and I usually don't know what'll make my happy until it does. But here's some general things. (This became long whoops)
  1. Ouran High School Host Club
    Basically my go-to cheer up thing. No idea when it became that but it has never failed to make me smile again.
  2. Flying sequences in How to Train Your Dragon
    Test Drive mostly. I drop everything when that scene is playing. As soon as the first few notes start I'm already happy.
  3. Finishing a good story
    Be it a show, movie, book or video game. I love this feeling. Most recent was an indie game called Undertale and it's almost ridiculous how much better I've felt since finishing it.
  4. Drawing
    Not the easiest thing to get back into but I still love it. Also other people's art as well.
  5. Animation
    Animation is my passion, which means this is basically a double-edged sword because it can also make me insanely angry.
  6. Cheering up my mum
    She doesn't get sad much but when she does cheering her up becomes my life mission. And it's really fun.
  7. Being able to geek out over stuff with my dad
    Our interests don't align up much.
  8. Memes
    I wish I was kidding. Internet shit posts have made me laugh to the point where I was in tears.
  9. Piano
    Playing piano. Piano in score music. Classical music. Piano covers. Piano in general.
  10. DC/Marvel Comics being nice to my favourite characters
    It's surprising how little this happens, so when it does it's basically Christmas come early. Why I even try trusting The Big Two is anyone's guess...
  11. Christmas
    I. Love. Christmas. This mostly arose when my family started becoming really apathetic and I decided to become Christmas cheer personified "turn those frowns upside-down". And my tiny!me's memories of Christmas in Germany, the atmosphere was amazing. Also (mainly) I just really like Christmas movies.
  12. Recordings of past antics
    I used to carry a video camera around with me. A lot of the stuff I recorded has become precious memories and watching them always brings a smile.
  13. Finding people with the same interests
    University was freaking amazing when I found people who loved animation on the same level as me. Also got to geek out over video games and manga which up until that point I never really had anyone for that.
  14. Score music
    A good chunk of my iPod and iTunes libraries is just score music. And I have an insane amount of music in those libraries.
  15. Cinematography
    Good use of cinematography makes me ridiculously happy. And ramble-y.
  16. Character development
    Especially going back and seeing how far a character has come, for good or bad. Though if it's closer to flanderisation, uh, not so much.
  17. Discovering new music
    Usually ends up on repeat for days.
  18. Re-reading/watching a favourite series
    Rediscovering why I fell in love the first time and repeating it all over again
  19. Bookstores
    Browsing the aisles. Finding that one book I've been searching for ages for. New releases having the next book in a series or by a favourite author I've been waiting for. Book sales. Author events. Second hand stores. The atmosphere.
  20. Packages being delivered at the door
    Things from overseas relatives and books/games arriving from online shopping. (Online shopping is addictive and I regret it)
  21. Little Things
    Both meaning miniaturised things and just "little things". It's always the little things that cheer me up in the most unexpected ways. This one is usually the most commented on with amusement by other people.
  22. My friends
    The most important. Their happiness makes me happy. Be they ones I've known most my life, met at high school or more recently at uni. They're all so important to me and it means a ridiculous amount they stick around. Friends were hard to keep when I was a kid and this is something I value the most.