jack all
A person who’s good at many things, but not great at any one of them. They’re like a jack all who’s not a jack all.
"He’s good at music, math, and pizza." "Yeah, he’s a jack all."
"He’s good at sports, sewing, and singing." "Yeah, he’s a jack all."
"He’s good at being annoying, eating, and sleeping." "Jack all, for sure."