On the main menu (after you have chosen a profile), there are five different ways to interact with Mac.

Hover your pointer around his right foot and he'll try to stomp on it
Hover about his left foot and he'll jump
Point at his left hand and he'll punch at you
Point at his face and he'll try to swat you away
Spin the pointer in circles around his face and he'll become dizzy!

Note: These only work while Mac's standing still, he won't react if you try to touch him while he's moving.