My DS2 (20 months old) likes to whack me too atm. I hold his hand away from me, say a firm "No!" and if he does it again he sits in time-out for 1 minute. I then make him say sorry, we have a cuddle and by then he has forgotten all about it.

I think it must be a stage they go through at this age to gain attention. It will pass, just be consistent no matter what you choose to do about it.