The backhander is better known as the pimp slap because pimps use it on their bitches to keep them in line. Since Will only has Jada and she has many other men on the side, this would make her the pimp and him the bitch in the relationship. This means he is not allowed to use the pimp slap, otherwise Jada will see him as another pimp and will have to bust a cap in his ass in case he becomes competition on her turf.