Advice on what or how to deal with boss that slapps employees?

I would just like advice on my boss feeling like he can just pop pple on the hand like were his 5 yr old children. I know that that is very unappropiate behavior on his part but what if ever I decided to could happen legally? A little more is hes a veterinarian...so he pops empolyees on the hand when were not holding the dogs to his perfect standards or our hand is In his way. I hate making a big deal out of things but its really starting to piss, me off. Two years ago my co worker quit the next day a after he slapped her hand for something dumb like handing him the wrong box or something. I think something should be done now...