One of my most recent ones is simply average Joes beating trained professionals with no explanation for his success other than, "Cuz he's the main character, duh!"
I saw a movie called "El Mariachi", where a penniless mariachi manages to take down an entire drug cartel. I could accept the idea of him outwitting them, but no, he just out-shoots them. He even beats one of them in a quickdraw. He's a friggin mariachi player, who's never killed a man or fired a gun in his life. How did he suddenly become a crack shot who can out-shoot an entire army of seasoned criminals?
The biggest offender in this movie was near the end, where he is lying on the ground and everyone is pointing their guns at him, when suddenly, he manages to reach to the side, grab a gun lying on the ground and shoot the leader before any of the ten guys pointing their guns at him can even think to pull the trigger. Bullshit!