Need advice: I have a 2.4 yo and he hits himself when upset

So this started when he was about 1.8 and he hit his mommy later he got upset and hit me (just a slap type thing with his hands on my hands) but this was when he was upset so I told him calmly you can’t hit people, it’s not nice, we don’t hit you, and so he said ok and hit himself instead... he slaps his hand with both hands at the same time...I got him to stop before by talking to him calmly. I recently I realized that I can get him to stop and laugh if I say don’t slap my pumpkin... But I can’t seem to get him to stop. He also does this when he wants a toy or is not getting his way.Anyone experienced this? Any advice on how to get him to stop?TIA via /r/Parenting https://ift.tt/2KDlAZh