If someone is slaphappier, they are happier than before, usually because something funny or silly happened.
Being slaphappier is a good feeling, like when you laugh a lot with your friends.
Examples:
After the joke, she was slaphappier than before.
The funny movie made everyone slaphappier.
He felt slaphappier after playing with his dog.
The silly hat made her even slaphappier.
When the clown fell down, everyone felt slaphappier.
The slaphappier he got, the more he laughed.