Happy Happy Joy Joy What do you say lets go play what does that mean?

Answer 1

Happy Happy Joy Joy was a song. It was in the cartoon the Ren and Stimpy Show. It was a spoof on children's nonsensical music and how kids can go crazy on that crap while it annoys parents.

So sounds like someone singing and wants to go play.

Answer 2

If your name is Happy (as in one of the seven dwarves) or Joy, then this is a direct invitation to have some fun. Otherwise, you could substitute anyone's name(s), i.e. Morty Morty Fred Fred What do you say, let's go play! and still issue the same invitation.
One response could be: Sad Sad Bummer Bummer I say no I won't go.