Aunt May v. Galactus
To make it fair, somewhat, this would be Galactus when he assumed human form in the Fantastic Four comicbook. He was a balding, middle aged man, who looked out of shape.
Even in human form, Galactus could easily defeat Aunt May. After all, isn't she really old and frail? However, Aunt May is currently living in the Avenger's Tower, and Tony Stark's security systems would easily neutralize the human Galactus before he could get to her.
But, what if he fought her in a dark alley? The fight would take maybe 30 seconds. He would push her down, kick her, break her hip, and then if he really wanted to hurt her, he could punch her in the face and break her jaw.
He wouldn't kill her, because this is Marvel comics... 😠