Very common but EXTERMELY frustraing behavior! Like everyone has said, be consisitent & don't let it show that he's getting you mad cuz that will just feed the fire. I know, easier said than done! I also agree w/offering lotsa positve praise, for even the smallest of acts. Like when he hugs you, thank him for the hug & let him know how much you like hugs instead of hits. We have 2 boys, 8 & 3.5 yrs & when they hurt someone, either physically or emotionally, I always point out how the other person is feeling, 'Look how sad so & so is cuz you hit them. See he's crying?' I want them to see the effect of their actions altho at 2.5, your son might still not get that but just keep pointing it out & it will start to sink in. But, as other have said, being consistent is key. Also, make sure whoever spends time w/him, grandparents, babysitters, daycare, dad ect, all displine for the same infractions so that he gets even if he's at grandma's house, hitting won't be tolerated & there will be consequences. Good luck!