When someone is doing something and you go up behind them and shake them vigorously while shouting, "CHALLENGE MODE!", causing them to totally screw up what they were doing.
It makes everything so much harder because it's challenge mode.
Katy was doing her homework when David came up and shook her shoulders crazily and shouted, "CHALLENGE MODE!!!!11!1111!!1!!!". Katy's homework was ruined because her pencil went all over the place.
Then Katy pwnd the nubcake.