well first off and most importantly... what kind of cookie?
I would scare people...
or murder someopne and they wouldnt be able to trace it back 2 me... nevermind to evil and and i would feel bad and there is noone I hate enough to kill...
Slap my geography teacher then go up to the girl I like and start screwing with her head. Like " The moon is made of cheese, would you like me to break your neck, i just cloned myself"
if anything, I would do nothing. the world is dangerous to an invisible person, you never know when some fat guy is going to sit on you, or if a car hits you, or what you are doing when the invisibility wears off. if anything, you could have some fun, but you'd eventually hate that nobody is noticing you.
if there were less dangerous scenarios for an invisible person, I'd play billiards, and then mess with people while they are trying to enjoy their evening.