What to do when discipline is funny?

OK, so my 2-year old is really a good kid so it hasn't been too often that we've needed to discipline him. But lately he has started hitting his nanny (and his Dad sometimes too) whenever he is frustrated... or really whenever he just feels like it, I think to get a response. He understands that it's not nice and says he's sorry right away, but keeps doing it. We feel like he should learn that there is a consequence connected to his actions--and hitting definitely isn't acceptable behavior.

We tried a time-out seat, but he just laughs and gets right back out. (In fact, if we ask him if he wants a time out, he says yes because he finds it so funny.) We tried putting him in his crib for time-out and closing the door, which made him cry the first few times, but now he knows we're coming back in so he just sits there waiting for us, often laughing. Should I try taking away a toy for bad behavior, or is he too young for that?

How do you discipine a smart toddler with a sense of humor??? I have no idea what else to try...