Come on. We all must have had that feeling where some part of the game's story made you feel a bit embarrassed. What part, exactly?
The cheesiest part had to be Arkham's fake villain laugh at the end of one mission. I forgot which one...16? 15? It's the one where he's entering the Devil World and is all, "Sparda's Power....will...be.....MIIINEE! AAAAHAAAHAAHAAHAHAHAAHAHAHAHAAAAHAAHAAHAAHAMWAAHAAHAHA!"
The second runner up would be Dante riding Lady's rocket after the Cerberus battle. That was funny, though, especially when he looked up at the exploded ceiling and lets out a "WOO!"