Once you hear it, you’ll never unhear it

What is the real lyric?

Someone did a cover of Happy and made it “Not Happy”, and this was what one of the lyrics were changed to (I listened to this cover so much that I don’t even know what the real lyrics were). For anyone interested, it’s actually done really nicely:
https://m.youtube.com/watch?v=NO6yaHggPf4

My brain went to the tune of “if you’re happy and you know it clap you’re hands”