Icchan is an extremely eccentric and immature fellow. He often jumps out of random places, shouting "Icchan go BOOM!" What does THAT tell you?
He also has this nasty habit of penalising poor Ogata. These penalties involving having a live octopus being stuck down his pants or being made to eat spaghetti through his nose. Icchan even went so far as to name an ugly angel after him and threatened to show it to everyone as a penalty.
That's just twisted.
Just about everytime Tamayo practices her martial arts techniques on poor Kotaro.