Get the Shark Costume from Joe, then go right into the break room. There are some Biologists here. Afterwards, go to every Biologist in the large room that leads into the cafeteria.
In the "World of Kelp" level. stop the Kelps that your sons shoot at you with an otter figure. After that mini-game ends, pick up the otter's head and put it on your head.
At the start of the last chapter, "Hot Concessions", allow the game to idle until you die one hundred times.