Hey guys and girls
I just stumbled upon an easier way of getting this with no hassle at all
-Beat the easy boss that appears
-Kill the first group of ninjas and other dudes in the first building you enter.
-You will then be in an area that has "grenades inside" written on the wall and you will see 2 arcade machines just to the left where you entered.
-Pick one up, and go to the door and hold x to open, you will notice when you enter the bathroom with the machine still in your hand, and luckily enough there are 2 enemies sitting there, so you get an easy target :)