"The man does not like groups."
Translation:Ní thaitníonn grúpaí leis an bhfear.
No, you don't. If you are using the negative particle ní, it will lenite the verb that it applies to. But in Ní maith liom, ní isn't the negative particle, and maith isn't a verb. This ní is the negative form of the copula (the positive version of the sentence is is maith leis ...) and this ní doesn't lenite.