Green’s Dictionary of Slang

(US) to vomit.

1964		J.D. MacDonald Deep Blue Goodby 105: ‘There's a kid in the apartment sleeping it off. She was whoopsing half the night from beer’.
1967		in S. Harris Hellhole 97: Maybe he got into a fight with someone or whoopsed up on himself.
1981		S. King Roadwork in Bachman Books (1995) 472: Hon, I think I’m going to whoopsie. Where’s the bathroom?