After their prank was successful, the friends wore goony smiles on their faces for the rest of the day.
Sing a mumble-gumble song[…] Do a loony-goony dance / ’Cross the kitchen floor1981, Shel Silverstein, “Put Something In”, in A Light in the Attic, Harper & Row:
goony
noun
Etymology * From goon + -y. Also as a shortened form of gooney.
1
Informal a goon; a foolish, stupid, silly, or awkward person.
2
Alternative Alternative form of gooney (gooney bird, the black-footed albatross).