Hack of all trades
Someone who is bad at a lot of different things
He’s not good at anything, a real hack of all trades.
Hack of All Trades
A "Hack of All Trades" is someone who isn't good at anything, unlike the saying "Jack of All Trades," meaning someone is seemingly good at everything, although not particularly having any expertise in anything.
Ms. Mediocre, hack of all trades. She's the master of none, since the start of her days.