You have a buddy. You can do anything to him. Most of the actions that can be done are going to most likely hurt him. Start off with grenades, punches, and hits. Every time you hit, tickle, or do stuff to your buddy, you get money to buy upgrades and skins. Slowly work your way to buying flamethrowers or a Bill Gates skin to make your enjoyment in inflicting pain/laughs on your buddy as maximized as possible.
Utilize your MOUSE to do everything.