The mass of the Earth is 5.972 × 10^24^, so you would need 5.972 × 10^20^ humans of 100 Kg each all turning in the same direction to make the Earth rotate 1% the other way (so about 597,200,000 trillion humans).

PS: I might be slightly wrong here as rotations have to do with angular momentum which is a bit more complicated than the linear kind because rotational inertia doesn't depende on mass alone, but the law of conservation of angular momentum does apply.